Bug 2513392 (CVE-2026-68145)

Summary: CVE-2026-68145 kernel: iomap: fix out-of-bounds bitmap_set() with zero-length range
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
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Priority: high    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel's iomap subsystem. An unsigned subtraction underflow occurs when `ifs_set_range_dirty()` or `ifs_set_range_uptodate()` are called with a zero-length range. This can lead to an out-of-bounds write via `bitmap_set()`, potentially allowing a local attacker to cause memory corruption or a denial of service.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Description OSIDB Bzimport 2026-08-10 12:34:50 UTC 
In the Linux kernel, the following vulnerability has been resolved:

iomap: fix out-of-bounds bitmap_set() with zero-length range

ifs_set_range_dirty() and ifs_set_range_uptodate() compute last_blk
as (off + len - 1) >> i_blkbits.  When off is 0 and len is 0, the
unsigned subtraction underflows to SIZE_MAX, producing a huge
last_blk and nr_blks value that causes bitmap_set() to write far
beyond the ifs->state allocation.

Regarding ifs_set_range_uptodate(), it is temporarily safe because len
cannot be passed in as 0. However, for ifs_set_range_dirty() this is
reachable from __iomap_write_end(): when copy_folio_from_iter_atomic()
returns 0 (e.g. user buffer fault) and the folio is already uptodate,
the guard at the top of __iomap_write_end() does not trigger because
!folio_test_uptodate() is false, and iomap_set_range_dirty() is called
with copied == 0.

Add a !len guard to both functions before the computation, so that a
zero-length range is a no-op.