From: Matthias Gerstner <matthias.gerstner@suse.de>
Date: Wed, 27 Dec 2023 13:01:59 +0000 (+0100)
Subject: pam_namespace: protect_dir(): use O_DIRECTORY to prevent local DoS situations
X-Git-Tag: accepted/tizen/base/20240530.091900^0
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=refs%2Fchanges%2F14%2F311114%2F1;p=platform%2Fupstream%2Fpam.git

pam_namespace: protect_dir(): use O_DIRECTORY to prevent local DoS situations

(backporting, CVE-2024-22356)

Without O_DIRECTORY the path crawling logic is subject to e.g. FIFOs
being placed in user controlled directories, causing the PAM module to
block indefinitely during `openat()`.

Pass O_DIRECTORY to cause the `openat()` to fail if the path does not
refer to a directory.

With this the check whether the final path element is a directory
becomes unnecessary, drop it.

Original: upstream, https://github.com/linux-pam/linux-pam/commit/031bb5a
Change-Id: I099e6d7fa62446160babf79d41fb19bfbfe5b186
Signed-off-by: Youngjae Cho <y0.cho@samsung.com>
(cherry picked from commit cb1ff0632d1d392606509c46d8fd25271a715825)
---

diff --git a/modules/pam_namespace/pam_namespace.c b/modules/pam_namespace/pam_namespace.c
index a40f05e..ed9b5fd 100644
--- a/modules/pam_namespace/pam_namespace.c
+++ b/modules/pam_namespace/pam_namespace.c
@@ -1012,7 +1012,7 @@ static int protect_dir(const char *path, mode_t mode, int do_mkdir,
 	int dfd = AT_FDCWD;
 	int dfd_next;
 	int save_errno;
-	int flags = O_RDONLY;
+	int flags = O_RDONLY | O_DIRECTORY;
 	int rv = -1;
 	struct stat st;
 
@@ -1066,22 +1066,6 @@ static int protect_dir(const char *path, mode_t mode, int do_mkdir,
 		rv = openat(dfd, dir, flags);
 	}
 
-	if (rv != -1) {
-		if (fstat(rv, &st) != 0) {
-			save_errno = errno;
-			close(rv);
-			rv = -1;
-			errno = save_errno;
-			goto error;
-		}
-		if (!S_ISDIR(st.st_mode)) {
-			close(rv);
-			errno = ENOTDIR;
-			rv = -1;
-			goto error;
-		}
-	}
-
 	if (flags & O_NOFOLLOW) {
 		/* we are inside user-owned dir - protect */
 		if (protect_mount(rv, p, idata) == -1) {