Commit 5ff232d31106 for kernel

commit 5ff232d31106f45ac87c3b64e1d35a0667777797
Author: Lincoln Wallace <locnnil0@gmail.com>
Date:   Mon Aug 3 10:50:21 2026 -0300

    ima: fix out-of-bounds read in xattr_verify()

    The digest-length check in xattr_verify() mixes int and size_t:

            if (xattr_len - sizeof(xattr_value->type) - hash_start >=
                            iint->ima_hash->length)

    sizeof() yields size_t, so the usual arithmetic conversions promote
    the whole left-hand side to unsigned 64-bit before the subtraction
    runs. For a truncated xattr this underflows instead of going negative:
    a 1-byte IMA_XATTR_DIGEST_NG xattr (xattr_len == 1, hash_start == 1)
    turns "1 - 1 - 1" into SIZE_MAX, which is trivially >= ima_hash->length.
    The check then passes and the following memcmp() reads
    iint->ima_hash->length bytes starting past the end of the buffer
    vfs_getxattr_alloc() allocated for it.

    Nothing upstream clamps xattr_len back into a safe range first:
    ima_get_hash_algo() only special-cases xattr_len < 2 to pick a default
    algorithm, and evm_verifyxattr() returns INTEGRITY_UNKNOWN rather than
    failing when no HMAC key is loaded, so a truncated security.ima value
    reaches the length check as-is.

    Rewrite the comparison so every operand stays a signed int and no
    implicit conversion to size_t can occur.

    Fixes: 3ea7a56067e6 ("ima: provide hash algo info in the xattr")
    Cc: stable@vger.kernel.org
    Signed-off-by: Lincoln Wallace <locnnil0@gmail.com>
    Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>

diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
index 18d0d9154317..ced2e131b061 100644
--- a/security/integrity/ima/ima_appraise.c
+++ b/security/integrity/ima/ima_appraise.c
@@ -274,8 +274,13 @@ static int xattr_verify(enum ima_hooks func, struct ima_iint_cache *iint,
 		} else {
 			set_bit(IMA_DIGSIG, &iint->atomic_flags);
 		}
-		if (xattr_len - sizeof(xattr_value->type) - hash_start >=
-				iint->ima_hash->length)
+		/*
+		 * Use addition, not subtraction: sizeof() forces unsigned
+		 * math and a short xattr_len would wrap around, bypassing
+		 * this bounds check.
+		 */
+		if (xattr_len >= (int)sizeof(xattr_value->type) + hash_start +
+				(int)iint->ima_hash->length)
 			/*
 			 * xattr length may be longer. md5 hash in previous
 			 * version occupied 20 bytes in xattr, instead of 16