[PATCH] ext4: xattr: fix null pointer deref in ext4_raw_inode()

[PATCH] ext4: xattr: fix null pointer deref in ext4_raw_inode()

[Karina Yankevich]

If ext4_get_inode_loc() fails (e.g. if it returns -EFSCORRUPTED),
iloc.bh will remain set to NULL. Since ext4_xattr_inode_dec_ref_all()
lacks error checking, this will lead to a null pointer dereference
in ext4_raw_inode(), called right after ext4_get_inode_loc().

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: c8e008b60492 ("ext4: ignore xattrs past end")
Signed-off-by: Karina Yankevich <k.yankevich@omp.ru>
Reviewed-by: Sergey Shtylyov <s.shtylyov@omp.ru>
---
 fs/ext4/xattr.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c
index ce7253b3f549..2e02efbddaac 100644
--- a/fs/ext4/xattr.c
+++ b/fs/ext4/xattr.c
@@ -1174,7 +1174,11 @@ ext4_xattr_inode_dec_ref_all(handle_t *handle, struct inode *parent,
 	if (block_csum)
 		end = (void *)bh->b_data + bh->b_size;
 	else {
-		ext4_get_inode_loc(parent, &iloc);
+		err = ext4_get_inode_loc(parent, &iloc);
+		if (err) {
+			EXT4_ERROR_INODE(parent, "parent inode loc (error %d)", err);
+			return;
+		}
 		end = (void *)ext4_raw_inode(&iloc) + EXT4_SB(parent->i_sb)->s_inode_size;
 	}
 
-- 
2.34.1

Re: [PATCH] ext4: xattr: fix null pointer deref in ext4_raw_inode()

[Markus Elfring]

> If ext4_get_inode_loc() fails (e.g. if it returns -EFSCORRUPTED),
…

Corresponding error detection seems to be missing so far.

Would another imperative wording become helpful for an improved change description?
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/submitting-patches.rst?h=v6.18-rc4#n94

Regards,
Markus

Re: [PATCH] ext4: xattr: fix null pointer deref in ext4_raw_inode()

[Baokun Li]

On 2025-10-22 17:32, Karina Yankevich wrote:
> If ext4_get_inode_loc() fails (e.g. if it returns -EFSCORRUPTED),
> iloc.bh will remain set to NULL. Since ext4_xattr_inode_dec_ref_all()
> lacks error checking, this will lead to a null pointer dereference
> in ext4_raw_inode(), called right after ext4_get_inode_loc().
>
> Found by Linux Verification Center (linuxtesting.org) with SVACE.
>
> Fixes: c8e008b60492 ("ext4: ignore xattrs past end")
> Signed-off-by: Karina Yankevich <k.yankevich@omp.ru>
> Reviewed-by: Sergey Shtylyov <s.shtylyov@omp.ru>

An error return at this point may lead to an inconsistent ea_inode
reference count. However, since the caller ext4_xattr_delete_inode()
has already loaded iloc.bh via ext4_get_inode_loc(), this almost never
fails.

Reviewed-by: Baokun Li <libaokun1@huawei.com>

> ---
>  fs/ext4/xattr.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c
> index ce7253b3f549..2e02efbddaac 100644
> --- a/fs/ext4/xattr.c
> +++ b/fs/ext4/xattr.c
> @@ -1174,7 +1174,11 @@ ext4_xattr_inode_dec_ref_all(handle_t *handle, struct inode *parent,
>  	if (block_csum)
>  		end = (void *)bh->b_data + bh->b_size;
>  	else {
> -		ext4_get_inode_loc(parent, &iloc);
> +		err = ext4_get_inode_loc(parent, &iloc);
> +		if (err) {
> +			EXT4_ERROR_INODE(parent, "parent inode loc (error %d)", err);
> +			return;
> +		}
>  		end = (void *)ext4_raw_inode(&iloc) + EXT4_SB(parent->i_sb)->s_inode_size;
>  	}
>  

Re: [PATCH] ext4: xattr: fix null pointer deref in ext4_raw_inode()

[Theodore Ts'o]

On Wed, 22 Oct 2025 12:32:53 +0300, Karina Yankevich wrote:
> If ext4_get_inode_loc() fails (e.g. if it returns -EFSCORRUPTED),
> iloc.bh will remain set to NULL. Since ext4_xattr_inode_dec_ref_all()
> lacks error checking, this will lead to a null pointer dereference
> in ext4_raw_inode(), called right after ext4_get_inode_loc().
> 
> Found by Linux Verification Center (linuxtesting.org) with SVACE.
> 
> [...]

Applied, thanks!

[1/1] ext4: xattr: fix null pointer deref in ext4_raw_inode()
      commit: b97cb7d6a051aa6ebd57906df0e26e9e36c26d14

Best regards,
-- 
Theodore Ts'o <tytso@mit.edu>