KMSAN reported a use of uninitialized value in `__is_extent_mergeable()`
 and `__is_back_mergeable()` via the read extent tree path.

The root cause is that `get_read_extent_info()` only initializes three
fields (`fofs`, `blk`, `len`) of `struct extent_info`, leaving the
remaining fields uninitialized. This leads to undefined behavior
when those fields are accessed later, especially during 
extent merging.

Fix it by zero-initializing the `extent_info` struct before population.

Reported-by: syzbot+b8c1d60e95df65e827d4@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=b8c1d60e95df65e827d4
Fixes: a28ef1f5aebe ("f2fs: maintain extent cache in separated file")
Signed-off-by: Abinash Singh <abinashsinghlalotra@gmail.com>
---
v3 : Added Fixes and Closes tags
---
 fs/f2fs/extent_cache.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/f2fs/extent_cache.c b/fs/f2fs/extent_cache.c
index cfe925a3d555..4ce19a310f38 100644
--- a/fs/f2fs/extent_cache.c
+++ b/fs/f2fs/extent_cache.c
@@ -414,7 +414,7 @@ void f2fs_init_read_extent_tree(struct inode *inode, struct folio *ifolio)
 	struct f2fs_extent *i_ext = &F2FS_INODE(&ifolio->page)->i_ext;
 	struct extent_tree *et;
 	struct extent_node *en;
-	struct extent_info ei;
+	struct extent_info ei = {0};
 
 	if (!__may_extent_tree(inode, EX_READ)) {
 		/* drop largest read extent */
-- 
2.43.0

On 6/25/25 01:09, Abinash Singh wrote:
> KMSAN reported a use of uninitialized value in `__is_extent_mergeable()`
>  and `__is_back_mergeable()` via the read extent tree path.
> 
> The root cause is that `get_read_extent_info()` only initializes three
> fields (`fofs`, `blk`, `len`) of `struct extent_info`, leaving the
> remaining fields uninitialized. This leads to undefined behavior
> when those fields are accessed later, especially during 
> extent merging.
> 
> Fix it by zero-initializing the `extent_info` struct before population.
> 
> Reported-by: syzbot+b8c1d60e95df65e827d4@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=b8c1d60e95df65e827d4
> Fixes: a28ef1f5aebe ("f2fs: maintain extent cache in separated file")

Should use this instead?

Fixes: 94afd6d6e525 ("f2fs: extent cache: support unaligned extent")

Reviewed-by: Chao Yu <chao@kernel.org>

Thanks,

> Signed-off-by: Abinash Singh <abinashsinghlalotra@gmail.com>
> ---
> v3 : Added Fixes and Closes tags
> ---
>  fs/f2fs/extent_cache.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/f2fs/extent_cache.c b/fs/f2fs/extent_cache.c
> index cfe925a3d555..4ce19a310f38 100644
> --- a/fs/f2fs/extent_cache.c
> +++ b/fs/f2fs/extent_cache.c
> @@ -414,7 +414,7 @@ void f2fs_init_read_extent_tree(struct inode *inode, struct folio *ifolio)
>  	struct f2fs_extent *i_ext = &F2FS_INODE(&ifolio->page)->i_ext;
>  	struct extent_tree *et;
>  	struct extent_node *en;
> -	struct extent_info ei;
> +	struct extent_info ei = {0};
>  
>  	if (!__may_extent_tree(inode, EX_READ)) {
>  		/* drop largest read extent */

KMSAN reported a use of uninitialized value in `__is_extent_mergeable()`
 and `__is_back_mergeable()` via the read extent tree path.

The root cause is that `get_read_extent_info()` only initializes three
fields (`fofs`, `blk`, `len`) of `struct extent_info`, leaving the
remaining fields uninitialized. This leads to undefined behavior
when those fields are accessed later, especially during
extent merging.

Fix it by zero-initializing the `extent_info` struct before population.

Reported-by: syzbot+b8c1d60e95df65e827d4@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=b8c1d60e95df65e827d4
Fixes: 94afd6d6e525 ("f2fs: extent cache: support unaligned extent")
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Abinash Singh <abinashsinghlalotra@gmail.com>
---
v4 : Added Reviewed-by and Corrected Fixes
---
 fs/f2fs/extent_cache.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/f2fs/extent_cache.c b/fs/f2fs/extent_cache.c
index cfe925a3d555..4ce19a310f38 100644
--- a/fs/f2fs/extent_cache.c
+++ b/fs/f2fs/extent_cache.c
@@ -414,7 +414,7 @@ void f2fs_init_read_extent_tree(struct inode *inode, struct folio *ifolio)
 	struct f2fs_extent *i_ext = &F2FS_INODE(&ifolio->page)->i_ext;
 	struct extent_tree *et;
 	struct extent_node *en;
-	struct extent_info ei;
+	struct extent_info ei = {0};
 
 	if (!__may_extent_tree(inode, EX_READ)) {
 		/* drop largest read extent */
-- 
2.43.0