CVE-2026-99109 — smb: client: reject SetEA requests that do not fit the request buffer

Affected: Linux

In the Linux kernel, the following vulnerability has been resolved:

smb: client: reject SetEA requests that do not fit the request buffer

CIFSSMBSetEA() copies the caller's extended attribute value into the SMB request buffer without checking that it fits. The requirement is stated in the source but was never implemented:

/*BB add length check to see if it would fit in negotiated SMB buffer size BB */ /* if (ea_value_len > buffer_size - 512 (enough for header)) */ if (ea_value_len) memcpy(parm_data->list.name + name_len + 1, ea_value, ea_value_len);

The only bound applied on the way in is in cifs_xattr_set():

#define MAX_EA_VALUE_SIZE CIFSMaxBufSize ... if (size > MAX_EA_VALUE_SIZE)

CIFSMaxBufSize is the full payload capacity of the buffer, so a value of exactly that size leaves no room for the SMB header, the TRANS2 parameter block, the fealist header and the EA name that are written ahead of it in the same object.

SendReceive() already enforces the correct limit on this very length:

if (in_len > CIFSMaxBufSize + MAX_CIFS_HDR_SIZE)

but it is called after the copy has taken place. An unprivileged setxattr(2) on an SMB1 mount with a 250-byte name and a 16384-byte value writes 16384 bytes starting 345 bytes into a 16588-byte cifs_request object, ending 141 bytes past it:

BUG: KASAN: slab-out-of-bounds in CIFSSMBSetEA+0xabc/0xde0 Write of size 16384 at addr ffff888003aa0159 by task init/68 __asan_memcpy+0x3c/0x60 CIFSSMBSetEA+0xabc/…

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CVE-2026-99109 — smb: client: reject SetEA requests that do not fit the request buffer