From 663d15697fe73b6e99d42537144ad2c1e1adbfbc Mon Sep 17 00:00:00 2001 From: Tristan Madani Date: Sat, 18 Apr 2026 03:54:57 +0800 Subject: [PATCH] ksmbd: use check_add_overflow() to prevent u16 DACL size overflow ANBZ: #34380 commit 8d5729350b236896f51379588d9a690b7fafb8db stable. commit 299f962c0b02d048fb45d248b4da493d03f3175d upstream. set_posix_acl_entries_dacl() and set_ntacl_dacl() accumulate ACE sizes in u16 variables. When a file has many POSIX ACL entries, the accumulated size can wrap past 65535, causing the pointer arithmetic (char *)pndace + *size to land within already-written ACEs. Subsequent writes then overwrite earlier entries, and pndacl->size gets a truncated value. Use check_add_overflow() at each accumulation point to detect the wrap before it corrupts the buffer, consistent with existing check_mul_overflow() usage elsewhere in smbacl.c. Cc: stable@vger.kernel.org Fixes: e2f34481b24d ("cifsd: add server-side procedures for SMB3") Signed-off-by: Tristan Madani Acked-by: Namjae Jeon Signed-off-by: Steve French Signed-off-by: Greg Kroah-Hartman Fixes: CVE-2026-31704 Assisted-by: PatchPilot Signed-off-by: Ferry Meng --- fs/smb/server/smbacl.c | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-) diff --git a/fs/smb/server/smbacl.c b/fs/smb/server/smbacl.c index b90f893762f4..693f724ba45e 100644 --- a/fs/smb/server/smbacl.c +++ b/fs/smb/server/smbacl.c @@ -595,6 +595,7 @@ static void set_posix_acl_entries_dacl(struct mnt_idmap *idmap, struct smb_sid *sid; struct smb_ace *ntace; int i, j; + u16 ace_sz; if (!fattr->cf_acls) goto posix_default_acl; @@ -639,8 +640,10 @@ static void set_posix_acl_entries_dacl(struct mnt_idmap *idmap, flags = 0x03; ntace = (struct smb_ace *)((char *)pndace + *size); - *size += fill_ace_for_sid(ntace, sid, ACCESS_ALLOWED, flags, + ace_sz = fill_ace_for_sid(ntace, sid, ACCESS_ALLOWED, flags, pace->e_perm, 0777); + if (check_add_overflow(*size, ace_sz, size)) + break; (*num_aces)++; if (pace->e_tag == ACL_USER) ntace->access_req |= @@ -649,8 +652,10 @@ static void set_posix_acl_entries_dacl(struct mnt_idmap *idmap, if (S_ISDIR(fattr->cf_mode) && (pace->e_tag == ACL_USER || pace->e_tag == ACL_GROUP)) { ntace = (struct smb_ace *)((char *)pndace + *size); - *size += fill_ace_for_sid(ntace, sid, ACCESS_ALLOWED, + ace_sz = fill_ace_for_sid(ntace, sid, ACCESS_ALLOWED, 0x03, pace->e_perm, 0777); + if (check_add_overflow(*size, ace_sz, size)) + break; (*num_aces)++; if (pace->e_tag == ACL_USER) ntace->access_req |= @@ -690,8 +695,10 @@ static void set_posix_acl_entries_dacl(struct mnt_idmap *idmap, } ntace = (struct smb_ace *)((char *)pndace + *size); - *size += fill_ace_for_sid(ntace, sid, ACCESS_ALLOWED, 0x0b, + ace_sz = fill_ace_for_sid(ntace, sid, ACCESS_ALLOWED, 0x0b, pace->e_perm, 0777); + if (check_add_overflow(*size, ace_sz, size)) + break; (*num_aces)++; if (pace->e_tag == ACL_USER) ntace->access_req |= @@ -727,7 +734,8 @@ static void set_ntacl_dacl(struct mnt_idmap *idmap, break; memcpy((char *)pndace + size, ntace, nt_ace_size); - size += nt_ace_size; + if (check_add_overflow(size, nt_ace_size, &size)) + break; aces_size -= nt_ace_size; ntace = (struct smb_ace *)((char *)ntace + nt_ace_size); num_aces++; -- Gitee