[PATCH 5.10.y v2 0/2] Backport 2 commits to fix a KASAN ext4 splat

[PATCH 5.10.y v2 0/2] Backport 2 commits to fix a KASAN ext4 splat

[David Nyström]

Backport commit:5701875f9609 ("ext4: fix out-of-bound read in
ext4_xattr_inode_dec_ref_all()" to linux 5.10 branch.
The fix depends on commit:69f3a3039b0d ("ext4: introduce ITAIL helper")
In order to make a clean backport on stable kernel, backport 2 commits.

It has a single merge conflict where static inline int, which changed 
to static int.

Signed-off-by: David Nyström <david.nystrom@est.tech>
---
Changes in v2:
- Resend identical patchset with correct "Upstream commit" denotation.
- Link to v1: https://patch.msgid.link/20251216-ext4_splat-v1-0-b76fd8748f44@est.tech

---
Ye Bin (2):
      ext4: introduce ITAIL helper
      ext4: fix out-of-bound read in ext4_xattr_inode_dec_ref_all()

 fs/ext4/inode.c |  5 +++++
 fs/ext4/xattr.c | 32 ++++----------------------------
 fs/ext4/xattr.h | 10 ++++++++++
 3 files changed, 19 insertions(+), 28 deletions(-)
---
base-commit: f964b940099f9982d723d4c77988d4b0dda9c165
change-id: 20251215-ext4_splat-f59c1acd9e88

Best regards,
--  
David Nyström <david.nystrom@est.tech>

[PATCH 5.10.y v2 1/2] ext4: introduce ITAIL helper

[David Nyström]

From: Ye Bin <yebin10@huawei.com>

[ Upstream commit 69f3a3039b0d0003de008659cafd5a1eaaa0a7a4 ]

Introduce ITAIL helper to get the bound of xattr in inode.

Signed-off-by: Ye Bin <yebin10@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://patch.msgid.link/20250208063141.1539283-2-yebin@huaweicloud.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: David Nyström <david.nystrom@est.tech>
---
 fs/ext4/xattr.c | 10 +++++-----
 fs/ext4/xattr.h |  3 +++
 2 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c
index fa8ce1c66d12..73a9b2934865 100644
--- a/fs/ext4/xattr.c
+++ b/fs/ext4/xattr.c
@@ -599,7 +599,7 @@ ext4_xattr_ibody_get(struct inode *inode, int name_index, const char *name,
 		return error;
 	raw_inode = ext4_raw_inode(&iloc);
 	header = IHDR(inode, raw_inode);
-	end = (void *)raw_inode + EXT4_SB(inode->i_sb)->s_inode_size;
+	end = ITAIL(inode, raw_inode);
 	error = xattr_check_inode(inode, header, end);
 	if (error)
 		goto cleanup;
@@ -744,7 +744,7 @@ ext4_xattr_ibody_list(struct dentry *dentry, char *buffer, size_t buffer_size)
 		return error;
 	raw_inode = ext4_raw_inode(&iloc);
 	header = IHDR(inode, raw_inode);
-	end = (void *)raw_inode + EXT4_SB(inode->i_sb)->s_inode_size;
+	end = ITAIL(inode, raw_inode);
 	error = xattr_check_inode(inode, header, end);
 	if (error)
 		goto cleanup;
@@ -826,7 +826,7 @@ int ext4_get_inode_usage(struct inode *inode, qsize_t *usage)
 			goto out;
 		raw_inode = ext4_raw_inode(&iloc);
 		header = IHDR(inode, raw_inode);
-		end = (void *)raw_inode + EXT4_SB(inode->i_sb)->s_inode_size;
+		end = ITAIL(inode, raw_inode);
 		ret = xattr_check_inode(inode, header, end);
 		if (ret)
 			goto out;
@@ -2215,7 +2215,7 @@ int ext4_xattr_ibody_find(struct inode *inode, struct ext4_xattr_info *i,
 	header = IHDR(inode, raw_inode);
 	is->s.base = is->s.first = IFIRST(header);
 	is->s.here = is->s.first;
-	is->s.end = (void *)raw_inode + EXT4_SB(inode->i_sb)->s_inode_size;
+	is->s.end = ITAIL(inode, raw_inode);
 	if (ext4_test_inode_state(inode, EXT4_STATE_XATTR)) {
 		error = xattr_check_inode(inode, header, is->s.end);
 		if (error)
@@ -2739,7 +2739,7 @@ int ext4_expand_extra_isize_ea(struct inode *inode, int new_extra_isize,
 	 */
 
 	base = IFIRST(header);
-	end = (void *)raw_inode + EXT4_SB(inode->i_sb)->s_inode_size;
+	end = ITAIL(inode, raw_inode);
 	min_offs = end - base;
 	total_ino = sizeof(struct ext4_xattr_ibody_header) + sizeof(u32);
 
diff --git a/fs/ext4/xattr.h b/fs/ext4/xattr.h
index e5e36bd11f05..9a596e19c2b1 100644
--- a/fs/ext4/xattr.h
+++ b/fs/ext4/xattr.h
@@ -68,6 +68,9 @@ struct ext4_xattr_entry {
 		((void *)raw_inode + \
 		EXT4_GOOD_OLD_INODE_SIZE + \
 		EXT4_I(inode)->i_extra_isize))
+#define ITAIL(inode, raw_inode) \
+	((void *)(raw_inode) + \
+	 EXT4_SB((inode)->i_sb)->s_inode_size)
 #define IFIRST(hdr) ((struct ext4_xattr_entry *)((hdr)+1))
 
 /*

-- 
2.48.1

[PATCH 5.10.y v2 2/2] ext4: fix out-of-bound read in ext4_xattr_inode_dec_ref_all()

[David Nyström]

From: Ye Bin <yebin10@huawei.com>

[ Upstream commit 5701875f9609b000d91351eaa6bfd97fe2f157f4 ]

There's issue as follows:
BUG: KASAN: use-after-free in ext4_xattr_inode_dec_ref_all+0x6ff/0x790
Read of size 4 at addr ffff88807b003000 by task syz-executor.0/15172

CPU: 3 PID: 15172 Comm: syz-executor.0
Call Trace:
 __dump_stack lib/dump_stack.c:82 [inline]
 dump_stack+0xbe/0xfd lib/dump_stack.c:123
 print_address_description.constprop.0+0x1e/0x280 mm/kasan/report.c:400
 __kasan_report.cold+0x6c/0x84 mm/kasan/report.c:560
 kasan_report+0x3a/0x50 mm/kasan/report.c:585
 ext4_xattr_inode_dec_ref_all+0x6ff/0x790 fs/ext4/xattr.c:1137
 ext4_xattr_delete_inode+0x4c7/0xda0 fs/ext4/xattr.c:2896
 ext4_evict_inode+0xb3b/0x1670 fs/ext4/inode.c:323
 evict+0x39f/0x880 fs/inode.c:622
 iput_final fs/inode.c:1746 [inline]
 iput fs/inode.c:1772 [inline]
 iput+0x525/0x6c0 fs/inode.c:1758
 ext4_orphan_cleanup fs/ext4/super.c:3298 [inline]
 ext4_fill_super+0x8c57/0xba40 fs/ext4/super.c:5300
 mount_bdev+0x355/0x410 fs/super.c:1446
 legacy_get_tree+0xfe/0x220 fs/fs_context.c:611
 vfs_get_tree+0x8d/0x2f0 fs/super.c:1576
 do_new_mount fs/namespace.c:2983 [inline]
 path_mount+0x119a/0x1ad0 fs/namespace.c:3316
 do_mount+0xfc/0x110 fs/namespace.c:3329
 __do_sys_mount fs/namespace.c:3540 [inline]
 __se_sys_mount+0x219/0x2e0 fs/namespace.c:3514
 do_syscall_64+0x33/0x40 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x67/0xd1

Memory state around the buggy address:
 ffff88807b002f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff88807b002f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff88807b003000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                   ^
 ffff88807b003080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88807b003100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff

Above issue happens as ext4_xattr_delete_inode() isn't check xattr
is valid if xattr is in inode.
To solve above issue call xattr_check_inode() check if xattr if valid
in inode. In fact, we can directly verify in ext4_iget_extra_inode(),
so that there is no divergent verification.

Fixes: e50e5129f384 ("ext4: xattr-in-inode support")
Signed-off-by: Ye Bin <yebin10@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://patch.msgid.link/20250208063141.1539283-3-yebin@huaweicloud.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: David Nyström <david.nystrom@est.tech>
---
 fs/ext4/inode.c |  5 +++++
 fs/ext4/xattr.c | 26 +-------------------------
 fs/ext4/xattr.h |  7 +++++++
 3 files changed, 13 insertions(+), 25 deletions(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 97f7cac0d349..719d9a2bc5a7 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -4650,6 +4650,11 @@ static inline int ext4_iget_extra_inode(struct inode *inode,
 	    *magic == cpu_to_le32(EXT4_XATTR_MAGIC)) {
 		int err;
 
+		err = xattr_check_inode(inode, IHDR(inode, raw_inode),
+					ITAIL(inode, raw_inode));
+		if (err)
+			return err;
+
 		ext4_set_inode_state(inode, EXT4_STATE_XATTR);
 		err = ext4_find_inline_data_nolock(inode);
 		if (!err && ext4_has_inline_data(inode))
diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c
index 73a9b2934865..16b9c87fd3d8 100644
--- a/fs/ext4/xattr.c
+++ b/fs/ext4/xattr.c
@@ -263,7 +263,7 @@ __ext4_xattr_check_block(struct inode *inode, struct buffer_head *bh,
 	__ext4_xattr_check_block((inode), (bh),  __func__, __LINE__)
 
 
-static int
+int
 __xattr_check_inode(struct inode *inode, struct ext4_xattr_ibody_header *header,
 			 void *end, const char *function, unsigned int line)
 {
@@ -280,9 +280,6 @@ __xattr_check_inode(struct inode *inode, struct ext4_xattr_ibody_header *header,
 	return error;
 }
 
-#define xattr_check_inode(inode, header, end) \
-	__xattr_check_inode((inode), (header), (end), __func__, __LINE__)
-
 static int
 xattr_find_entry(struct inode *inode, struct ext4_xattr_entry **pentry,
 		 void *end, int name_index, const char *name, int sorted)
@@ -600,9 +597,6 @@ ext4_xattr_ibody_get(struct inode *inode, int name_index, const char *name,
 	raw_inode = ext4_raw_inode(&iloc);
 	header = IHDR(inode, raw_inode);
 	end = ITAIL(inode, raw_inode);
-	error = xattr_check_inode(inode, header, end);
-	if (error)
-		goto cleanup;
 	entry = IFIRST(header);
 	error = xattr_find_entry(inode, &entry, end, name_index, name, 0);
 	if (error)
@@ -734,7 +728,6 @@ ext4_xattr_ibody_list(struct dentry *dentry, char *buffer, size_t buffer_size)
 	struct ext4_xattr_ibody_header *header;
 	struct ext4_inode *raw_inode;
 	struct ext4_iloc iloc;
-	void *end;
 	int error;
 
 	if (!ext4_test_inode_state(inode, EXT4_STATE_XATTR))
@@ -744,14 +737,9 @@ ext4_xattr_ibody_list(struct dentry *dentry, char *buffer, size_t buffer_size)
 		return error;
 	raw_inode = ext4_raw_inode(&iloc);
 	header = IHDR(inode, raw_inode);
-	end = ITAIL(inode, raw_inode);
-	error = xattr_check_inode(inode, header, end);
-	if (error)
-		goto cleanup;
 	error = ext4_xattr_list_entries(dentry, IFIRST(header),
 					buffer, buffer_size);
 
-cleanup:
 	brelse(iloc.bh);
 	return error;
 }
@@ -815,7 +803,6 @@ int ext4_get_inode_usage(struct inode *inode, qsize_t *usage)
 	struct ext4_xattr_ibody_header *header;
 	struct ext4_xattr_entry *entry;
 	qsize_t ea_inode_refs = 0;
-	void *end;
 	int ret;
 
 	lockdep_assert_held_read(&EXT4_I(inode)->xattr_sem);
@@ -826,10 +813,6 @@ int ext4_get_inode_usage(struct inode *inode, qsize_t *usage)
 			goto out;
 		raw_inode = ext4_raw_inode(&iloc);
 		header = IHDR(inode, raw_inode);
-		end = ITAIL(inode, raw_inode);
-		ret = xattr_check_inode(inode, header, end);
-		if (ret)
-			goto out;
 
 		for (entry = IFIRST(header); !IS_LAST_ENTRY(entry);
 		     entry = EXT4_XATTR_NEXT(entry))
@@ -2217,9 +2200,6 @@ int ext4_xattr_ibody_find(struct inode *inode, struct ext4_xattr_info *i,
 	is->s.here = is->s.first;
 	is->s.end = ITAIL(inode, raw_inode);
 	if (ext4_test_inode_state(inode, EXT4_STATE_XATTR)) {
-		error = xattr_check_inode(inode, header, is->s.end);
-		if (error)
-			return error;
 		/* Find the named attribute. */
 		error = xattr_find_entry(inode, &is->s.here, is->s.end,
 					 i->name_index, i->name, 0);
@@ -2743,10 +2723,6 @@ int ext4_expand_extra_isize_ea(struct inode *inode, int new_extra_isize,
 	min_offs = end - base;
 	total_ino = sizeof(struct ext4_xattr_ibody_header) + sizeof(u32);
 
-	error = xattr_check_inode(inode, header, end);
-	if (error)
-		goto cleanup;
-
 	ifree = ext4_xattr_free_space(base, &min_offs, base, &total_ino);
 	if (ifree >= isize_diff)
 		goto shift;
diff --git a/fs/ext4/xattr.h b/fs/ext4/xattr.h
index 9a596e19c2b1..cbf235422aec 100644
--- a/fs/ext4/xattr.h
+++ b/fs/ext4/xattr.h
@@ -210,6 +210,13 @@ extern int ext4_xattr_ibody_set(handle_t *handle, struct inode *inode,
 extern struct mb_cache *ext4_xattr_create_cache(void);
 extern void ext4_xattr_destroy_cache(struct mb_cache *);
 
+extern int
+__xattr_check_inode(struct inode *inode, struct ext4_xattr_ibody_header *header,
+		    void *end, const char *function, unsigned int line);
+
+#define xattr_check_inode(inode, header, end) \
+	__xattr_check_inode((inode), (header), (end), __func__, __LINE__)
+
 #ifdef CONFIG_EXT4_FS_SECURITY
 extern int ext4_init_security(handle_t *handle, struct inode *inode,
 			      struct inode *dir, const struct qstr *qstr);

-- 
2.48.1

Re: [PATCH 5.10.y v2 0/2] Backport 2 commits to fix a KASAN ext4 splat

[Greg KH]

On Wed, Dec 17, 2025 at 10:55:56AM +0100, David Nyström wrote:
> Backport commit:5701875f9609 ("ext4: fix out-of-bound read in
> ext4_xattr_inode_dec_ref_all()" to linux 5.10 branch.
> The fix depends on commit:69f3a3039b0d ("ext4: introduce ITAIL helper")
> In order to make a clean backport on stable kernel, backport 2 commits.
> 
> It has a single merge conflict where static inline int, which changed 
> to static int.
> 
> Signed-off-by: David Nyström <david.nystrom@est.tech>
> ---
> Changes in v2:
> - Resend identical patchset with correct "Upstream commit" denotation.
> - Link to v1: https://patch.msgid.link/20251216-ext4_splat-v1-0-b76fd8748f44@est.tech
> 
> ---
> Ye Bin (2):
>       ext4: introduce ITAIL helper
>       ext4: fix out-of-bound read in ext4_xattr_inode_dec_ref_all()
> 
>  fs/ext4/inode.c |  5 +++++
>  fs/ext4/xattr.c | 32 ++++----------------------------
>  fs/ext4/xattr.h | 10 ++++++++++
>  3 files changed, 19 insertions(+), 28 deletions(-)
> ---
> base-commit: f964b940099f9982d723d4c77988d4b0dda9c165
> change-id: 20251215-ext4_splat-f59c1acd9e88
> 
> Best regards,
> --  
> David Nyström <david.nystrom@est.tech>
> 
> 

We can't take patches only for an older kernel tree, and not newer ones.
Otherwise you will have a regression when upgrading.

Please resend patches for all applicable kernel trees and we will be
glad to queue them all up.

thanks

greg k-h