CVE-2026-64074fs/statmount: fix slab out-of-bounds write in statmount_mnt_idmap

Official description

In the Linux kernel, the following vulnerability has been resolved: fs/statmount: fix slab out-of-bounds write in statmount_mnt_idmap statmount_mnt_idmap() writes one mapping with seq_printf() and then manually advances seq->count to include the NUL separator. If seq_printf() overflows, seq_set_overflow() sets seq->count to seq->size. The manual seq->count++ changes this to seq->size + 1. seq_has_overflowed() then no longer detects the overflow. The corrupted count returns to statmount_string(), which later executes: seq->buf[seq->count++] = '\0'; This causes a 1-byte NULL out-of-bounds write on the dynamically allocated seq buffer. Fix this by checking for overflow immediately after seq_printf().

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/e37ea2c6f17f273813ea4e8e94c102591d598ce1
• https://git.kernel.org/stable/c/93614949dc86f068e3c32c32cf1ee2a2323177a7
• https://git.kernel.org/stable/c/a3bf0f28d4ba16e1f35f8c983bb04426b87e2a78