[PATCH v2 0/2] lib/base64: decode fixes

[PATCH v2 0/2] lib/base64: decode fixes

[Josh Law]

Two small fixes for lib/base64.c:

1. base64_decode() writes a decoded byte to the output buffer before
   validating the input in the trailing-bytes path. Move the validity
   checks before any writes so dst is untouched on invalid input.

2. The @padding kernel-doc for base64_decode() was copy-pasted from
   base64_encode() and describes the wrong direction.

v2: fix bogus Fixes tag in patch 1

Josh Law (2):
  lib/base64: validate before writing in decode tail path
  lib/base64: fix copy-pasted @padding doc in base64_decode()

 lib/base64.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

-- 
2.34.1

[PATCH v2 1/2] lib/base64: validate before writing in decode tail path

[Josh Law]

The trailing-bytes path in base64_decode() writes a decoded byte to
the output buffer before checking whether the input characters are
valid. If the input is malformed, garbage is written to dst before the
function returns -1.

Move the validity checks before any writes so the output buffer is
left untouched on invalid input.

Fixes: 9c7d3cf94d33 ("lib/base64: rework encode/decode for speed and stricter validation")
Signed-off-by: Josh Law <objecting@objecting.org>
---
 lib/base64.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/lib/base64.c b/lib/base64.c
index 41961a444028..20dacee25f65 100644
--- a/lib/base64.c
+++ b/lib/base64.c
@@ -168,15 +168,16 @@ int base64_decode(const char *src, int srclen, u8 *dst, bool padding, enum base6
 		return -1;
 
 	val = (base64_rev_tables[s[0]] << 12) | (base64_rev_tables[s[1]] << 6);
-	*bp++ = val >> 10;
 
 	if (srclen == 2) {
 		if (val & 0x800003ff)
 			return -1;
+		*bp++ = val >> 10;
 	} else {
 		val |= base64_rev_tables[s[2]];
 		if (val & 0x80000003)
 			return -1;
+		*bp++ = val >> 10;
 		*bp++ = val >> 2;
 	}
 	return bp - dst;
-- 
2.34.1

[PATCH v2 2/2] lib/base64: fix copy-pasted @padding doc in base64_decode()

[Josh Law]

The @padding kernel-doc for base64_decode() says "whether to append
'=' padding characters", which was copy-pasted from base64_encode().
In the decode context, it controls whether the input is expected to
include padding, not whether to append it.

Signed-off-by: Josh Law <objecting@objecting.org>
---
 lib/base64.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/base64.c b/lib/base64.c
index 20dacee25f65..325c7332b049 100644
--- a/lib/base64.c
+++ b/lib/base64.c
@@ -122,7 +122,7 @@ EXPORT_SYMBOL_GPL(base64_encode);
  * @src: the string to decode.  Doesn't need to be NUL-terminated.
  * @srclen: the length of @src in bytes
  * @dst: (output) the decoded binary data
- * @padding: whether to append '=' padding characters
+ * @padding: whether the input is expected to include '=' padding characters
  * @variant: which base64 variant to use
  *
  * Decodes a string using the selected Base64 variant.
-- 
2.34.1