CVE-2026-31705ksmbd: fix out-of-bounds write in smb2_get_ea() EA alignment

Official description

In the Linux kernel, the following vulnerability has been resolved: ksmbd: fix out-of-bounds write in smb2_get_ea() EA alignment smb2_get_ea() applies 4-byte alignment padding via memset() after writing each EA entry. The bounds check on buf_free_len is performed before the value memcpy, but the alignment memset fires unconditionally afterward with no check on remaining space. When the EA value exactly fills the remaining buffer (buf_free_len == 0 after value subtraction), the alignment memset writes 1-3 NUL bytes past the buf_free_len boundary. In compound requests where the response buffer is shared across commands, the first command (e.g., READ) can consume most of the buffer, leaving a tight remainder for the QUERY_INFO EA response. The alignment memset then overwrites past the physical kvmalloc allocation into adjacent kernel heap memory. Add a bounds check before the alignment memset to ensure buf_free_len can accommodate the padding bytes. This is the same bug pattern fixed by commit beef2634f81f ("ksmbd: fix potencial OOB in get_file_all_info() for compound requests") and commit fda9522ed6af ("ksmbd: fix OOB write in QUERY_INFO for compound requests"), both of which added bounds checks before unconditional writes in QUERY_INFO response handlers.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/ddbbc8b2a09dd2cfed90871313e3691ae1db08a2
• https://git.kernel.org/stable/c/ffbce350c6fd1e99116ea57383b9031717e36d3b
• https://git.kernel.org/stable/c/98f3de6ef4efbd899348d333f0902dc4ff14380c
• https://git.kernel.org/stable/c/790304c02bf9bd7b8171feda4294d6e62d32ae8f
• https://git.kernel.org/stable/c/922d48fe8c19f388ffa2f709f33acaae4e408de2
• https://git.kernel.org/stable/c/30010c952077a1c89ecdd71fc4d574c75a8f5617
• https://cert-portal.siemens.com/productcert/html/ssa-784472.html