In the Linux kernel, the following vulnerability has been resolved:
ext4: refresh inline data size before write operations
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:
- ext4_get_max_inline_size() reads i_inline_size = 60 (correct)
- Size check passes for 50-byte write
- [Another thread adds xattr, i_inline_size changes to 40]
- ext4_write_lock_xattr() acquires lock
- ext4_update_inline_data() uses stale i_inline_size = 60
- Attempts to write 50 bytes but only 40 bytes actually available
- 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.