Fix CVE-2026-4878

debian/changelog

@@ -1,3 +1,11 @@
+libcap2 (1:2.75-10deepin1) unstable; urgency=medium
+
+  * Apply patches from upstream:
+    - Address a potential TOCTOU race condition in cap_set_file()
+    Fixes: CVE-2026-4878
+
+ -- Tianyu Chen <sweetyfish@deepin.org>  Thu, 09 Apr 2026 14:34:21 +0800
+
 libcap2 (1:2.75-10) unstable; urgency=medium
 
   * d/rules: Fix typo in override_dh_auto_clean

debian/patches/Address-a-potential-TOCTOU-race-condition-in-cap_set_file.patch

@@ -0,0 +1,155 @@
+From: "Andrew G. Morgan" <morgan@kernel.org>
+Date: Thu, 12 Mar 2026 07:38:05 -0700
+Subject: Address a potential TOCTOU race condition in cap_set_file().
+
+This issue was researched and reported by Ali Raza (@locus-x64). It
+has been assigned CVE-2026-4878.
+
+The finding is that while cap_set_file() checks if a file is a regular
+file before applying or removing a capability attribute, a small
+window existed after that check when the filepath could be overwritten
+either with new content or a symlink to some other file. To do this
+would imply that the caller of cap_set_file() was directing it to a
+directory over which a local attacker has write access, and performed
+the operation frequently enough that an attacker had a non-negligible
+chance of exploiting the race condition. The code now locks onto the
+intended file, eliminating the race condition.
+
+Signed-off-by: Andrew G. Morgan <morgan@kernel.org>
+---
+ libcap/cap_file.c  | 69 ++++++++++++++++++++++++++++++++++++++++++++++--------
+ progs/quicktest.sh | 14 ++++++++++-
+ 2 files changed, 72 insertions(+), 11 deletions(-)
+
+diff --git a/libcap/cap_file.c b/libcap/cap_file.c
+index 0bc07f7..f02bf9f 100644
+--- a/libcap/cap_file.c
++++ b/libcap/cap_file.c
+@@ -8,8 +8,13 @@
+ #define _DEFAULT_SOURCE
+ #endif
+
++#ifndef _GNU_SOURCE
++#define _GNU_SOURCE
++#endif
++
+ #include <sys/types.h>
+ #include <byteswap.h>
++#include <fcntl.h>
+ #include <sys/stat.h>
+ #include <unistd.h>
+
+@@ -322,26 +327,70 @@ int cap_set_file(const char *filename, cap_t cap_d)
+     struct vfs_ns_cap_data rawvfscap;
+     int sizeofcaps;
+     struct stat buf;
++    char fdpath[64];
++    int fd, ret;
++
++    _cap_debug("setting filename capabilities");
++    fd = open(filename, O_RDONLY|O_NOFOLLOW);
++    if (fd >= 0) {
++	ret = cap_set_fd(fd, cap_d);
++	close(fd);
++	return ret;
++    }
+
+-    if (lstat(filename, &buf) != 0) {
+-	_cap_debug("unable to stat file [%s]", filename);
++    /*
++     * Attempting to set a file capability on a file the process can't
++     * read the content of. This is considered a non-standard use case
++     * and the following (slower) code is complicated because it is
++     * trying to avoid a TOCTOU race condition.
++     */
++
++    fd = open(filename, O_PATH|O_NOFOLLOW);
++    if (fd < 0) {
++	_cap_debug("cannot find file at path [%s]", filename);
++	return -1;
++    }
++    if (fstat(fd, &buf) != 0) {
++	_cap_debug("unable to stat file [%s] descriptor %d",
++		   filename, fd);
++	close(fd);
+ 	return -1;
+     }
+     if (S_ISLNK(buf.st_mode) || !S_ISREG(buf.st_mode)) {
+-	_cap_debug("file [%s] is not a regular file", filename);
++	_cap_debug("file [%s] descriptor %d for non-regular file",
++		   filename, fd);
++	close(fd);
+ 	errno = EINVAL;
+ 	return -1;
+     }
+
+-    if (cap_d == NULL) {
+-	_cap_debug("removing filename capabilities");
+-	return removexattr(filename, XATTR_NAME_CAPS);
++    /*
++     * While the fd remains open, this named file is locked to the
++     * origin regular file. The size of the fdpath variable is
++     * sufficient to support a 160+ bit number.
++     */
++    if (snprintf(fdpath, sizeof(fdpath), "/proc/self/fd/%d", fd)
++	>= sizeof(fdpath)) {
++	_cap_debug("file descriptor too large %d", fd);
++	errno = EINVAL;
++	ret = -1;
++
++    } else if (cap_d == NULL) {
++	_cap_debug("dropping file caps on [%s] via [%s]",
++		   filename, fdpath);
++	ret = removexattr(fdpath, XATTR_NAME_CAPS);
++
+     } else if (_fcaps_save(&rawvfscap, cap_d, &sizeofcaps) != 0) {
+-	return -1;
+-    }
++	_cap_debug("problem converting cap_d to vfscap format");
++	ret = -1;
+
+-    _cap_debug("setting filename capabilities");
+-    return setxattr(filename, XATTR_NAME_CAPS, &rawvfscap, sizeofcaps, 0);
++    } else {
++	_cap_debug("setting filename capabilities");
++	ret = setxattr(fdpath, XATTR_NAME_CAPS, &rawvfscap,
++		       sizeofcaps, 0);
++    }
++    close(fd);
++    return ret;
+ }
+
+ /*
+diff --git a/progs/quicktest.sh b/progs/quicktest.sh
+index e6c48e6..5dc72f9 100755
+--- a/progs/quicktest.sh
++++ b/progs/quicktest.sh
+@@ -148,7 +148,19 @@ pass_capsh --caps="cap_setpcap=p" --inh=cap_chown --current
+ pass_capsh --strict --caps="cap_chown=p" --inh=cap_chown --current
+
+ # change the way the capability is obtained (make it inheritable)
++chmod 0000 ./privileged
+ ./setcap cap_setuid,cap_setgid=ei ./privileged
++if [ $? -ne 0 ]; then
++    echo "FAILED to set file capability"
++    exit 1
++fi
++chmod 0755 ./privileged
++ln -s privileged unprivileged
++./setcap -r ./unprivileged
++if [ $? -eq 0 ]; then
++    echo "FAILED by removing a capability from a symlinked file"
++    exit 1
++fi
+
+ # Note, the bounding set (edited with --drop) only limits p
+ # capabilities, not i's.
+@@ -246,7 +258,7 @@ EOF
+     pass_capsh --iab='!%cap_chown,^cap_setpcap,cap_setuid'
+     fail_capsh --mode=PURE1E --iab='!%cap_chown,^cap_setuid'
+ fi
+-/bin/rm -f ./privileged
++/bin/rm -f ./privileged ./unprivileged
+
+ echo "testing namespaced file caps"
+

debian/patches/series

@@ -5,3 +5,4 @@ Glibc-needs-a-constant-to-be-defined-for-puts-to-work.patch
 Add-support-for-some-less-mainstream-architectures.patch
 Extend-support-further-to-__m68k__-and-possibly-__sparc__.patch
 Be-more-systematic-using-the-kernel-signal-handler-APIs.patch
+Address-a-potential-TOCTOU-race-condition-in-cap_set_file.patch