[1/3] btrfs: fix use-after-free on inode when scanning root during em shrinking

Commit Message

Filipe Manana Feb. 16, 2025, 1:16 p.m. UTC

From: Filipe Manana <[e-mail]>

At btrfs_scan_root() we are accessing the inode's root (and fs_info) in a
call to btrfs_fs_closing() after we have scheduled the inode for a delayed
iput, and that can result in a use-after-free on the inode in case the
cleaner kthread does the iput before we dereference the inode in the call
to btrfs_fs_closing().

Fix this by using the fs_info stored already in a local variable instead
of doing inode->root->fs_info.

Fixes: 102044384056 ("btrfs: make the extent map shrinker run asynchronously as a work queue job")
CC: [e-mail] # 6.13+
Tested-by: Ivan Shapovalov <[e-mail]>
Link: https://lore.kernel.org/linux-btrfs/[e-mail]/
Signed-off-by: Filipe Manana <[e-mail]>
---
 fs/btrfs/extent_map.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

Comments

Johannes Thumshirn Feb. 17, 2025, 5:47 p.m. UTC | #1

Looks good,
Reviewed-by: Johannes Thumshirn <[e-mail]>

Patch

diff --git a/fs/btrfs/extent_map.c b/fs/btrfs/extent_map.c
index 67ce85ff0ae2..bee1b94a1049 100644
--- a/fs/btrfs/extent_map.c
+++ b/fs/btrfs/extent_map.c
@@ -1222,8 +1222,7 @@  static long btrfs_scan_root(struct btrfs_root *root, struct btrfs_em_shrink_ctx
 		fs_info->em_shrinker_last_ino = btrfs_ino(inode);
 		btrfs_add_delayed_iput(inode);
 
-		if (ctx->scanned >= ctx->nr_to_scan ||
-		    btrfs_fs_closing(inode->root->fs_info))
+		if (ctx->scanned >= ctx->nr_to_scan || btrfs_fs_closing(fs_info))
 			break;
 
 		cond_resched();