CVE-2026-45858ext4: don't zero the entire extent if EXT4_EXT_DATA_PARTIAL_VALID1

Official description

In the Linux kernel, the following vulnerability has been resolved: ext4: don't zero the entire extent if EXT4_EXT_DATA_PARTIAL_VALID1 When allocating initialized blocks from a large unwritten extent, or when splitting an unwritten extent during end I/O and converting it to initialized, there is currently a potential issue of stale data if the extent needs to be split in the middle. 0 A B N [UUUUUUUUUUUU] U: unwritten extent [--DDDDDDDD--] D: valid data |<- ->| ----> this range needs to be initialized ext4_split_extent() first try to split this extent at B with EXT4_EXT_DATA_ENTIRE_VALID1 and EXT4_EXT_MAY_ZEROOUT flag set, but ext4_split_extent_at() failed to split this extent due to temporary lack of space. It zeroout B to N and mark the entire extent from 0 to N as written. 0 A B N [WWWWWWWWWWWW] W: written extent [SSDDDDDDDDZZ] Z: zeroed, S: stale data ext4_split_extent() then try to split this extent at A with EXT4_EXT_DATA_VALID2 flag set. This time, it split successfully and left a stale written extent from 0 to A. 0 A B N [WW|WWWWWWWWWW] [SS|DDDDDDDDZZ] Fix this by pass EXT4_EXT_DATA_PARTIAL_VALID1 to ext4_split_extent_at() when splitting at B, don't convert the entire extent to written and left it as unwritten after zeroing out B to N. The remaining work is just like the standard two-part split. ext4_split_extent() will pass the EXT4_EXT_DATA_VALID2 flag when it calls ext4_split_extent_at() for the second time, allowing it to properly handle the split. If the split is successful, it will keep extent from 0 to A as unwritten.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/58ddae5d77b1db3a27b891c75a8fa120239ac092
• https://git.kernel.org/stable/c/d17857b4fb9ba5745b59be0ef38fd532991fccbf
• https://git.kernel.org/stable/c/d67c8ecf3d8fda9b8ef80e6f665d84b6d6ac9d88
• https://git.kernel.org/stable/c/7015fcf473796e1d2d876f241bd9e0c36f3d4eef
• https://git.kernel.org/stable/c/1bf6974822d1dba86cf11b5f05498581cf3488a2