FAILED: patch "[PATCH] bootconfig: fix NULL-pointer arithmetic in" failed to apply to 5.15-stable tree

FAILED: patch "[PATCH] bootconfig: fix NULL-pointer arithmetic in" failed to apply to 5.15-stable tree

[gregkh]

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x dec4d8118c179b3d12bca7e609054c6011c4f2ce
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026072113-skintight-barometer-812e@gregkh' --subject-prefix 'PATCH 5.15.y' 'HEAD^..'

Possible dependencies:



thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From dec4d8118c179b3d12bca7e609054c6011c4f2ce Mon Sep 17 00:00:00 2001
From: Breno Leitao <leitao@debian.org>
Date: Fri, 26 Jun 2026 05:50:10 -0700
Subject: [PATCH] bootconfig: fix NULL-pointer arithmetic in
 xbc_snprint_cmdline()

xbc_snprint_cmdline() is meant to be called twice: first with
buf=NULL, size=0 to probe the rendered length, then with a real
buffer to fill it (the standard snprintf() two-pass pattern). The
probe call makes the function compute "buf + size" (NULL + 0) and,
on every iteration, advance "buf += ret" from that NULL base and
pass the result back into snprintf().

Pointer arithmetic on a NULL pointer is undefined behavior. It is
harmless in the in-kernel callers today, but the follow-up patches
run this same code in the userspace tools/bootconfig parser at kernel
build time, where host UBSan / FORTIFY_SOURCE abort the build.

Track a running written length (size_t) instead of mutating @buf, and
only form "buf + len" when @buf is non-NULL. snprintf(NULL, 0, ...)
is itself well defined and returns the would-be length, so the
two-pass "probe then fill" usage returns identical byte counts.

Link: https://lore.kernel.org/all/20260626-bootconfig_using_tools-v7-1-24ab72139c29@debian.org/

Fixes: 51887d03aca1 ("bootconfig: init: Allow admin to use bootconfig for kernel command line")
Cc: stable@vger.kernel.org
Signed-off-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

diff --git a/lib/bootconfig.c b/lib/bootconfig.c
index f445b7703fdd..2ed9ee3dc81c 100644
--- a/lib/bootconfig.c
+++ b/lib/bootconfig.c
@@ -427,10 +427,18 @@ static char xbc_namebuf[XBC_KEYLEN_MAX] __initdata;
 int __init xbc_snprint_cmdline(char *buf, size_t size, struct xbc_node *root)
 {
 	struct xbc_node *knode, *vnode;
-	char *end = buf + size;
 	const char *val, *q;
+	size_t len = 0;
 	int ret;
 
+	/*
+	 * Track the running written length rather than advancing @buf, so we
+	 * never form "buf + size" or "buf += ret" while @buf is NULL (the
+	 * size-probe call passes buf=NULL, size=0). NULL pointer arithmetic
+	 * is undefined behavior and trips host UBSan / FORTIFY_SOURCE when
+	 * this renderer runs at kernel build time. snprintf(NULL, 0, ...)
+	 * itself is well defined and returns the would-be length.
+	 */
 	xbc_node_for_each_key_value(root, knode, val) {
 		ret = xbc_node_compose_key_after(root, knode,
 					xbc_namebuf, XBC_KEYLEN_MAX);
@@ -439,10 +447,11 @@ int __init xbc_snprint_cmdline(char *buf, size_t size, struct xbc_node *root)
 
 		vnode = xbc_node_get_child(knode);
 		if (!vnode) {
-			ret = snprintf(buf, rest(buf, end), "%s ", xbc_namebuf);
+			ret = snprintf(buf ? buf + len : NULL, rest(len, size),
+				       "%s ", xbc_namebuf);
 			if (ret < 0)
 				return ret;
-			buf += ret;
+			len += ret;
 			continue;
 		}
 		xbc_array_for_each_value(vnode, val) {
@@ -452,15 +461,15 @@ int __init xbc_snprint_cmdline(char *buf, size_t size, struct xbc_node *root)
 			 * whitespace.
 			 */
 			q = strpbrk(val, " \t\r\n") ? "\"" : "";
-			ret = snprintf(buf, rest(buf, end), "%s=%s%s%s ",
-				       xbc_namebuf, q, val, q);
+			ret = snprintf(buf ? buf + len : NULL, rest(len, size),
+				       "%s=%s%s%s ", xbc_namebuf, q, val, q);
 			if (ret < 0)
 				return ret;
-			buf += ret;
+			len += ret;
 		}
 	}
 
-	return buf - (end - size);
+	return len;
 }
 #undef rest
 

[PATCH 5.15.y 1/3] bootconfig: do not put quotes on cmdline items unless necessary

[Sasha Levin]

From: Rasmus Villemoes <linux@rasmusvillemoes.dk>

[ Upstream commit 212f863fa8811c780abacc1d0404c573fdc0a2de ]

When trying to migrate to using bootconfig to embed the kernel's and
PID1's command line with the kernel image itself, and so allowing changing
that without modifying the bootloader, I noticed that /proc/cmdline
changed from e.g.

  console=ttymxc0,115200n8 cma=128M quiet -- --log-level=notice

to

  console="ttymxc0,115200n8" cma="128M" quiet -- --log-level="notice"

The kernel parameters are parsed just fine, and the quotes are indeed
stripped from the actual argv[] given to PID1.  However, the quoting
doesn't really serve any purpose and looks excessive, and might confuse
some (naive) userspace tool trying to parse /proc/cmdline.  So do not
quote the value unless it contains whitespace.

Link: https://lkml.kernel.org/r/20240320101952.62135-1-linux@rasmusvillemoes.dk
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Stable-dep-of: dec4d8118c17 ("bootconfig: fix NULL-pointer arithmetic in xbc_snprint_cmdline()")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 init/main.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/init/main.c b/init/main.c
index 4e9c76a0e5a478..f9e98fb3a3e098 100644
--- a/init/main.c
+++ b/init/main.c
@@ -328,7 +328,7 @@ static int __init xbc_snprint_cmdline(char *buf, size_t size,
 {
 	struct xbc_node *knode, *vnode;
 	char *end = buf + size;
-	const char *val;
+	const char *val, *q;
 	int ret;
 
 	xbc_node_for_each_key_value(root, knode, val) {
@@ -346,8 +346,14 @@ static int __init xbc_snprint_cmdline(char *buf, size_t size,
 			continue;
 		}
 		xbc_array_for_each_value(vnode, val) {
-			ret = snprintf(buf, rest(buf, end), "%s=\"%s\" ",
-				       xbc_namebuf, val);
+			/*
+			 * For prettier and more readable /proc/cmdline, only
+			 * quote the value when necessary, i.e. when it contains
+			 * whitespace.
+			 */
+			q = strpbrk(val, " \t\r\n") ? "\"" : "";
+			ret = snprintf(buf, rest(buf, end), "%s=%s%s%s ",
+				       xbc_namebuf, q, val, q);
 			if (ret < 0)
 				return ret;
 			buf += ret;
-- 
2.53.0

[PATCH 5.15.y 2/3] bootconfig: move xbc_snprint_cmdline() to lib/bootconfig.c

[Sasha Levin]

From: Breno Leitao <leitao@debian.org>

[ Upstream commit 5a643e4623238e14b03d75ca0d4eda0645720cee ]

Move xbc_snprint_cmdline() from init/main.c to lib/bootconfig.c so the
function (and its xbc_namebuf scratch buffer) becomes part of the shared
parser library. tools/bootconfig already compiles lib/bootconfig.c
directly, which lets a follow-up patch reuse the same renderer in the
userspace tool to convert a bootconfig file into a flat cmdline string
at build time.

No functional change.

Link: https://lore.kernel.org/all/20260508-bootconfig_using_tools-v1-1-1132219aa773@debian.org/

Signed-off-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Stable-dep-of: dec4d8118c17 ("bootconfig: fix NULL-pointer arithmetic in xbc_snprint_cmdline()")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 include/linux/bootconfig.h |  3 ++
 init/main.c                | 45 ------------------------------
 lib/bootconfig.c           | 56 ++++++++++++++++++++++++++++++++++++++
 3 files changed, 59 insertions(+), 45 deletions(-)

diff --git a/include/linux/bootconfig.h b/include/linux/bootconfig.h
index 5296fbb8408cae..2105a94294ca6a 100644
--- a/include/linux/bootconfig.h
+++ b/include/linux/bootconfig.h
@@ -254,6 +254,9 @@ static inline struct xbc_node * __init xbc_node_get_subkey(struct xbc_node *node
 int __init xbc_node_compose_key_after(struct xbc_node *root,
 			struct xbc_node *node, char *buf, size_t size);
 
+/* Render key/value pairs under @root as a flat cmdline string */
+int __init xbc_snprint_cmdline(char *buf, size_t size, struct xbc_node *root);
+
 /**
  * xbc_node_compose_key() - Compose full key string of the XBC node
  * @node: An XBC node.
diff --git a/init/main.c b/init/main.c
index f9e98fb3a3e098..c86df2005204aa 100644
--- a/init/main.c
+++ b/init/main.c
@@ -319,51 +319,6 @@ static void * __init get_boot_config_from_initrd(u32 *_size, u32 *_csum)
 
 #ifdef CONFIG_BOOT_CONFIG
 
-static char xbc_namebuf[XBC_KEYLEN_MAX] __initdata;
-
-#define rest(dst, end) ((end) > (dst) ? (end) - (dst) : 0)
-
-static int __init xbc_snprint_cmdline(char *buf, size_t size,
-				      struct xbc_node *root)
-{
-	struct xbc_node *knode, *vnode;
-	char *end = buf + size;
-	const char *val, *q;
-	int ret;
-
-	xbc_node_for_each_key_value(root, knode, val) {
-		ret = xbc_node_compose_key_after(root, knode,
-					xbc_namebuf, XBC_KEYLEN_MAX);
-		if (ret < 0)
-			return ret;
-
-		vnode = xbc_node_get_child(knode);
-		if (!vnode) {
-			ret = snprintf(buf, rest(buf, end), "%s ", xbc_namebuf);
-			if (ret < 0)
-				return ret;
-			buf += ret;
-			continue;
-		}
-		xbc_array_for_each_value(vnode, val) {
-			/*
-			 * For prettier and more readable /proc/cmdline, only
-			 * quote the value when necessary, i.e. when it contains
-			 * whitespace.
-			 */
-			q = strpbrk(val, " \t\r\n") ? "\"" : "";
-			ret = snprintf(buf, rest(buf, end), "%s=%s%s%s ",
-				       xbc_namebuf, q, val, q);
-			if (ret < 0)
-				return ret;
-			buf += ret;
-		}
-	}
-
-	return buf - (end - size);
-}
-#undef rest
-
 /* Make an extra command line under given key word */
 static char * __init xbc_make_cmdline(const char *key)
 {
diff --git a/lib/bootconfig.c b/lib/bootconfig.c
index 9873c6372adca6..f497087e6fb1c9 100644
--- a/lib/bootconfig.c
+++ b/lib/bootconfig.c
@@ -339,6 +339,62 @@ const char * __init xbc_node_find_next_key_value(struct xbc_node *root,
 		return "";	/* No value key */
 }
 
+static char xbc_namebuf[XBC_KEYLEN_MAX] __initdata;
+
+#define rest(dst, end) ((end) > (dst) ? (end) - (dst) : 0)
+
+/**
+ * xbc_snprint_cmdline() - Render bootconfig keys under @root as a cmdline string
+ * @buf: Destination buffer (may be NULL when @size is 0 to query the length)
+ * @size: Size of @buf in bytes
+ * @root: Subtree root whose key=value pairs should be rendered
+ *
+ * Walk all key/value pairs under @root and emit them as a space-separated
+ * cmdline string into @buf. Values containing whitespace are quoted with
+ * double quotes. Returns the number of bytes that would be written if @buf
+ * were large enough (matching snprintf semantics), or a negative errno on
+ * failure.
+ */
+int __init xbc_snprint_cmdline(char *buf, size_t size, struct xbc_node *root)
+{
+	struct xbc_node *knode, *vnode;
+	char *end = buf + size;
+	const char *val, *q;
+	int ret;
+
+	xbc_node_for_each_key_value(root, knode, val) {
+		ret = xbc_node_compose_key_after(root, knode,
+					xbc_namebuf, XBC_KEYLEN_MAX);
+		if (ret < 0)
+			return ret;
+
+		vnode = xbc_node_get_child(knode);
+		if (!vnode) {
+			ret = snprintf(buf, rest(buf, end), "%s ", xbc_namebuf);
+			if (ret < 0)
+				return ret;
+			buf += ret;
+			continue;
+		}
+		xbc_array_for_each_value(vnode, val) {
+			/*
+			 * For prettier and more readable /proc/cmdline, only
+			 * quote the value when necessary, i.e. when it contains
+			 * whitespace.
+			 */
+			q = strpbrk(val, " \t\r\n") ? "\"" : "";
+			ret = snprintf(buf, rest(buf, end), "%s=%s%s%s ",
+				       xbc_namebuf, q, val, q);
+			if (ret < 0)
+				return ret;
+			buf += ret;
+		}
+	}
+
+	return buf - (end - size);
+}
+#undef rest
+
 /* XBC parse and tree build */
 
 static int __init xbc_init_node(struct xbc_node *node, char *data, u32 flag)
-- 
2.53.0

[PATCH 5.15.y 3/3] bootconfig: fix NULL-pointer arithmetic in xbc_snprint_cmdline()

[Sasha Levin]

From: Breno Leitao <leitao@debian.org>

[ Upstream commit dec4d8118c179b3d12bca7e609054c6011c4f2ce ]

xbc_snprint_cmdline() is meant to be called twice: first with
buf=NULL, size=0 to probe the rendered length, then with a real
buffer to fill it (the standard snprintf() two-pass pattern). The
probe call makes the function compute "buf + size" (NULL + 0) and,
on every iteration, advance "buf += ret" from that NULL base and
pass the result back into snprintf().

Pointer arithmetic on a NULL pointer is undefined behavior. It is
harmless in the in-kernel callers today, but the follow-up patches
run this same code in the userspace tools/bootconfig parser at kernel
build time, where host UBSan / FORTIFY_SOURCE abort the build.

Track a running written length (size_t) instead of mutating @buf, and
only form "buf + len" when @buf is non-NULL. snprintf(NULL, 0, ...)
is itself well defined and returns the would-be length, so the
two-pass "probe then fill" usage returns identical byte counts.

Link: https://lore.kernel.org/all/20260626-bootconfig_using_tools-v7-1-24ab72139c29@debian.org/

Fixes: 51887d03aca1 ("bootconfig: init: Allow admin to use bootconfig for kernel command line")
Cc: stable@vger.kernel.org
Signed-off-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 lib/bootconfig.c | 23 ++++++++++++++++-------
 1 file changed, 16 insertions(+), 7 deletions(-)

diff --git a/lib/bootconfig.c b/lib/bootconfig.c
index f497087e6fb1c9..ac878b861c0b92 100644
--- a/lib/bootconfig.c
+++ b/lib/bootconfig.c
@@ -358,10 +358,18 @@ static char xbc_namebuf[XBC_KEYLEN_MAX] __initdata;
 int __init xbc_snprint_cmdline(char *buf, size_t size, struct xbc_node *root)
 {
 	struct xbc_node *knode, *vnode;
-	char *end = buf + size;
 	const char *val, *q;
+	size_t len = 0;
 	int ret;
 
+	/*
+	 * Track the running written length rather than advancing @buf, so we
+	 * never form "buf + size" or "buf += ret" while @buf is NULL (the
+	 * size-probe call passes buf=NULL, size=0). NULL pointer arithmetic
+	 * is undefined behavior and trips host UBSan / FORTIFY_SOURCE when
+	 * this renderer runs at kernel build time. snprintf(NULL, 0, ...)
+	 * itself is well defined and returns the would-be length.
+	 */
 	xbc_node_for_each_key_value(root, knode, val) {
 		ret = xbc_node_compose_key_after(root, knode,
 					xbc_namebuf, XBC_KEYLEN_MAX);
@@ -370,10 +378,11 @@ int __init xbc_snprint_cmdline(char *buf, size_t size, struct xbc_node *root)
 
 		vnode = xbc_node_get_child(knode);
 		if (!vnode) {
-			ret = snprintf(buf, rest(buf, end), "%s ", xbc_namebuf);
+			ret = snprintf(buf ? buf + len : NULL, rest(len, size),
+				       "%s ", xbc_namebuf);
 			if (ret < 0)
 				return ret;
-			buf += ret;
+			len += ret;
 			continue;
 		}
 		xbc_array_for_each_value(vnode, val) {
@@ -383,15 +392,15 @@ int __init xbc_snprint_cmdline(char *buf, size_t size, struct xbc_node *root)
 			 * whitespace.
 			 */
 			q = strpbrk(val, " \t\r\n") ? "\"" : "";
-			ret = snprintf(buf, rest(buf, end), "%s=%s%s%s ",
-				       xbc_namebuf, q, val, q);
+			ret = snprintf(buf ? buf + len : NULL, rest(len, size),
+				       "%s=%s%s%s ", xbc_namebuf, q, val, q);
 			if (ret < 0)
 				return ret;
-			buf += ret;
+			len += ret;
 		}
 	}
 
-	return buf - (end - size);
+	return len;
 }
 #undef rest
 
-- 
2.53.0

Re: [PATCH 5.15.y 1/3] bootconfig: do not put quotes on cmdline items unless necessary

[Masami Hiramatsu]

Thanks Sasha for backporting the series!

These look good to me!

On Tue, 28 Jul 2026 18:17:48 -0400
Sasha Levin <sashal@kernel.org> wrote:

> From: Rasmus Villemoes <linux@rasmusvillemoes.dk>
> 
> [ Upstream commit 212f863fa8811c780abacc1d0404c573fdc0a2de ]
> 
> When trying to migrate to using bootconfig to embed the kernel's and
> PID1's command line with the kernel image itself, and so allowing changing
> that without modifying the bootloader, I noticed that /proc/cmdline
> changed from e.g.
> 
>   console=ttymxc0,115200n8 cma=128M quiet -- --log-level=notice
> 
> to
> 
>   console="ttymxc0,115200n8" cma="128M" quiet -- --log-level="notice"
> 
> The kernel parameters are parsed just fine, and the quotes are indeed
> stripped from the actual argv[] given to PID1.  However, the quoting
> doesn't really serve any purpose and looks excessive, and might confuse
> some (naive) userspace tool trying to parse /proc/cmdline.  So do not
> quote the value unless it contains whitespace.
> 
> Link: https://lkml.kernel.org/r/20240320101952.62135-1-linux@rasmusvillemoes.dk
> Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
> Cc: Masami Hiramatsu <mhiramat@kernel.org>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> Stable-dep-of: dec4d8118c17 ("bootconfig: fix NULL-pointer arithmetic in xbc_snprint_cmdline()")
> Signed-off-by: Sasha Levin <sashal@kernel.org>
> ---
>  init/main.c | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/init/main.c b/init/main.c
> index 4e9c76a0e5a478..f9e98fb3a3e098 100644
> --- a/init/main.c
> +++ b/init/main.c
> @@ -328,7 +328,7 @@ static int __init xbc_snprint_cmdline(char *buf, size_t size,
>  {
>  	struct xbc_node *knode, *vnode;
>  	char *end = buf + size;
> -	const char *val;
> +	const char *val, *q;
>  	int ret;
>  
>  	xbc_node_for_each_key_value(root, knode, val) {
> @@ -346,8 +346,14 @@ static int __init xbc_snprint_cmdline(char *buf, size_t size,
>  			continue;
>  		}
>  		xbc_array_for_each_value(vnode, val) {
> -			ret = snprintf(buf, rest(buf, end), "%s=\"%s\" ",
> -				       xbc_namebuf, val);
> +			/*
> +			 * For prettier and more readable /proc/cmdline, only
> +			 * quote the value when necessary, i.e. when it contains
> +			 * whitespace.
> +			 */
> +			q = strpbrk(val, " \t\r\n") ? "\"" : "";
> +			ret = snprintf(buf, rest(buf, end), "%s=%s%s%s ",
> +				       xbc_namebuf, q, val, q);
>  			if (ret < 0)
>  				return ret;
>  			buf += ret;
> -- 
> 2.53.0
> 


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>