6.18-stable review patch. If anyone has any objections, please let me know.
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From: Deepanshu Kartikey kartikey406@gmail.com
commit 892e1cf17555735e9d021ab036c36bc7b58b0e3b upstream.
The cached ei->i_inline_size can become stale between the initial size check and when ext4_update_inline_data()/ext4_create_inline_data() use it. Although ext4_get_max_inline_size() reads the correct value at the time of the check, concurrent xattr operations can modify i_inline_size before ext4_write_lock_xattr() is acquired.
This causes ext4_update_inline_data() and ext4_create_inline_data() to work with stale capacity values, leading to a BUG_ON() crash in ext4_write_inline_data():
kernel BUG at fs/ext4/inline.c:1331! BUG_ON(pos + len > EXT4_I(inode)->i_inline_size);
The race window: 1. ext4_get_max_inline_size() reads i_inline_size = 60 (correct) 2. Size check passes for 50-byte write 3. [Another thread adds xattr, i_inline_size changes to 40] 4. ext4_write_lock_xattr() acquires lock 5. ext4_update_inline_data() uses stale i_inline_size = 60 6. Attempts to write 50 bytes but only 40 bytes actually available 7. BUG_ON() triggers
Fix this by recalculating i_inline_size via ext4_find_inline_data_nolock() immediately after acquiring xattr_sem. This ensures ext4_update_inline_data() and ext4_create_inline_data() work with current values that are protected from concurrent modifications.
This is similar to commit a54c4613dac1 ("ext4: fix race writing to an inline_data file while its xattrs are changing") which fixed i_inline_off staleness. This patch addresses the related i_inline_size staleness issue.
Reported-by: syzbot+f3185be57d7e8dda32b8@syzkaller.appspotmail.com Link: https://syzkaller.appspot.com/bug?extid=f3185be57d7e8dda32b8 Cc: stable@kernel.org Signed-off-by: Deepanshu Kartikey kartikey406@gmail.com Message-ID: 20251020060936.474314-1-kartikey406@gmail.com Signed-off-by: Theodore Ts'o tytso@mit.edu Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/ext4/inline.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)
--- a/fs/ext4/inline.c +++ b/fs/ext4/inline.c @@ -418,7 +418,12 @@ static int ext4_prepare_inline_data(hand return -ENOSPC;
ext4_write_lock_xattr(inode, &no_expand); - + /* + * ei->i_inline_size may have changed since the initial check + * if other xattrs were added. Recalculate to ensure + * ext4_update_inline_data() validates against current capacity. + */ + (void) ext4_find_inline_data_nolock(inode); if (ei->i_inline_off) ret = ext4_update_inline_data(handle, inode, len); else