From af92ee994cc7f7e83a41c2025f32257a2f82a7ef Mon Sep 17 00:00:00 2001 From: Ferry Meng Date: Mon, 11 May 2026 21:18:16 +0800 Subject: [PATCH] ksmbd: fix SID memory leak in set_posix_acl_entries_dacl() on overflow Commit 299f962c0b02 ("ksmbd: use check_add_overflow() to prevent u16 DACL size overflow") added check_add_overflow() guards that break out of the ACE-building loops in set_posix_acl_entries_dacl() when the accumulated DACL size would wrap past 65535. However, each iteration allocates a struct smb_sid via kmalloc_obj() at the top of the loop and relies on the kfree(sid) call at the end of the loop body (the 'pass_same_sid' label in the first loop, and the explicit kfree at the tail of the second loop) to release it. The newly introduced 'break' statements bypass those kfree() calls, leaking the sid buffer every time an overflow is detected. A malicious or malformed file with enough POSIX ACL entries to trip the overflow check will leak one or more struct smb_sid allocations on every request that touches the file's DACL, providing a trivial kernel memory exhaustion vector. Free sid before breaking out of the loops to plug the leak. Fixes: 299f962c0b02 ("ksmbd: use check_add_overflow() to prevent u16 DACL size overflow") Cc: stable@vger.kernel.org Signed-off-by: Ferry Meng Acked-by: Namjae Jeon Signed-off-by: Steve French --- fs/smb/server/smbacl.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-) diff --git a/fs/smb/server/smbacl.c b/fs/smb/server/smbacl.c index c1d1f34581d6..9161e9d7ed24 100644 --- a/fs/smb/server/smbacl.c +++ b/fs/smb/server/smbacl.c @@ -643,8 +643,10 @@ static void set_posix_acl_entries_dacl(struct mnt_idmap *idmap, ntace = (struct smb_ace *)((char *)pndace + *size); ace_sz = fill_ace_for_sid(ntace, sid, ACCESS_ALLOWED, flags, pace->e_perm, 0777); - if (check_add_overflow(*size, ace_sz, size)) + if (check_add_overflow(*size, ace_sz, size)) { + kfree(sid); break; + } (*num_aces)++; if (pace->e_tag == ACL_USER) ntace->access_req |= @@ -655,8 +657,10 @@ static void set_posix_acl_entries_dacl(struct mnt_idmap *idmap, ntace = (struct smb_ace *)((char *)pndace + *size); ace_sz = fill_ace_for_sid(ntace, sid, ACCESS_ALLOWED, 0x03, pace->e_perm, 0777); - if (check_add_overflow(*size, ace_sz, size)) + if (check_add_overflow(*size, ace_sz, size)) { + kfree(sid); break; + } (*num_aces)++; if (pace->e_tag == ACL_USER) ntace->access_req |= @@ -698,8 +702,10 @@ static void set_posix_acl_entries_dacl(struct mnt_idmap *idmap, ntace = (struct smb_ace *)((char *)pndace + *size); ace_sz = fill_ace_for_sid(ntace, sid, ACCESS_ALLOWED, 0x0b, pace->e_perm, 0777); - if (check_add_overflow(*size, ace_sz, size)) + if (check_add_overflow(*size, ace_sz, size)) { + kfree(sid); break; + } (*num_aces)++; if (pace->e_tag == ACL_USER) ntace->access_req |=