ext4: refresh inline data size before write operations

Overview

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:

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.

Affected

• Linux >= 67cf5b09a46f72e048501b84996f2f77bc42e947 < 54ab81ae5f218452e64470cd8a8139bb5880fe2b
• Linux >= 67cf5b09a46f72e048501b84996f2f77bc42e947 < 43bf001f0fe4e59bba47c897505222f959f4a1cc
• Linux >= 67cf5b09a46f72e048501b84996f2f77bc42e947 < 89c2c41f0974e530b2d032c3695095aa0559adb1
• Linux >= 67cf5b09a46f72e048501b84996f2f77bc42e947 < 1687a055a555347b002f406676a1aaae4668f242
• Linux >= 67cf5b09a46f72e048501b84996f2f77bc42e947 < 210ac60a86a3ad2c76ae60e0dc71c34af6e7ea0b
• Linux >= 67cf5b09a46f72e048501b84996f2f77bc42e947 < ca43ea29b4c4d2764aec8a26cffcfb677a871e6e
• Linux >= 67cf5b09a46f72e048501b84996f2f77bc42e947 < 58df743faf21ceb1880f930aa5dd428e2a5e415d
• Linux >= 67cf5b09a46f72e048501b84996f2f77bc42e947 < 892e1cf17555735e9d021ab036c36bc7b58b0e3b
• Linux 3.8

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.