From: "Hugo SIMELIERE (Schneider Electric)" <[email protected]>
Pick patch from [1] as 2.39.x upstream backport of [2] mentioned in Debian report in [3]. [1] https://github.com/util-linux/util-linux/commit/79164668a412b71fcb1495c7d299cc5e9741fa30 [2] https://github.com/util-linux/util-linux/commit/0ba0f14caa812349424df0da00ac2d97fee9d972 [3] https://security-tracker.debian.org/tracker/CVE-2026-27456 Signed-off-by: Hugo SIMELIERE (Schneider Electric) <[email protected]> Reviewed-by: Bruno VERNAY <[email protected]> --- meta/recipes-core/util-linux/util-linux.inc | 1 + .../util-linux/CVE-2026-27456.patch | 115 ++++++++++++++++++ 2 files changed, 116 insertions(+) create mode 100644 meta/recipes-core/util-linux/util-linux/CVE-2026-27456.patch diff --git a/meta/recipes-core/util-linux/util-linux.inc b/meta/recipes-core/util-linux/util-linux.inc index 4797682c5d..8380419634 100644 --- a/meta/recipes-core/util-linux/util-linux.inc +++ b/meta/recipes-core/util-linux/util-linux.inc @@ -46,6 +46,7 @@ SRC_URI = "${KERNELORG_MIRROR}/linux/utils/util-linux/v${MAJOR_VERSION}/util-lin file://sys-utils-hwclock-rtc-fix-pointer-usage.patch \ file://CVE-2025-14104-01.patch \ file://CVE-2025-14104-02.patch \ + file://CVE-2026-27456.patch \ " SRC_URI[sha256sum] = "7b6605e48d1a49f43cc4b4cfc59f313d0dd5402fa40b96810bd572e167dfed0f" diff --git a/meta/recipes-core/util-linux/util-linux/CVE-2026-27456.patch b/meta/recipes-core/util-linux/util-linux/CVE-2026-27456.patch new file mode 100644 index 0000000000..4a5fef26d3 --- /dev/null +++ b/meta/recipes-core/util-linux/util-linux/CVE-2026-27456.patch @@ -0,0 +1,115 @@ +From af0b619f8eb15f738c69e33e0bb3a794e9cccf17 Mon Sep 17 00:00:00 2001 +From: Karel Zak <[email protected]> +Date: Thu, 19 Feb 2026 13:59:46 +0100 +Subject: [PATCH] loopdev: add LOOPDEV_FL_NOFOLLOW to prevent symlink attacks + +Add a new LOOPDEV_FL_NOFOLLOW flag for loop device context that +prevents symlink following in both path canonicalization and file open. + +When set: +- loopcxt_set_backing_file() uses strdup() instead of + ul_canonicalize_path() (which calls realpath() and follows symlinks) +- loopcxt_setup_device() adds O_NOFOLLOW to open() flags + +The flag is set for non-root (restricted) mount operations in +libmount's loop device hook. This prevents a TOCTOU race condition +where an attacker could replace the backing file (specified in +/etc/fstab) with a symlink to an arbitrary root-owned file between +path resolution and open(). + +Vulnerable Code Flow: + + mount /mnt/point (non-root, SUID) + mount.c: sanitize_paths() on user args (mountpoint only) + mnt_context_mount() + mnt_context_prepare_mount() + mnt_context_apply_fstab() <-- source path from fstab + hooks run at MNT_STAGE_PREP_SOURCE + hook_loopdev.c: setup_loopdev() + backing_file = fstab source path ("/home/user/disk.img") + loopcxt_set_backing_file() <-- calls realpath() as ROOT + ul_canonicalize_path() <-- follows symlinks! + loopcxt_setup_device() + open(lc->filename, O_RDWR|O_CLOEXEC) <-- no O_NOFOLLOW + +Two vulnerabilities in the path: + +1) loopcxt_set_backing_file() calls ul_canonicalize_path() which uses + realpath() -- this follows symlinks as euid=0. If the attacker swaps + the file to a symlink before this call, lc->filename becomes the + resolved target path (e.g., /root/secret.img). + +2) loopcxt_setup_device() opens lc->filename without O_NOFOLLOW. Even + if canonicalization happened correctly, the file can be swapped to a + symlink between canonicalize and open. + +CVE: CVE-2026-27456 +Upstream-Status: Backport [https://github.com/util-linux/util-linux/commit/79164668a412b71fcb1495c7d299cc5e9741fa30] + +Addresses: https://github.com/util-linux/util-linux/security/advisories/GHSA-qq4x-vfq4-9h9g +Signed-off-by: Karel Zak <[email protected]> +(cherry picked from commit 5e390467b26a3cf3fecc04e1a0d482dff3162fc4) +(cherry picked from commit 79164668a412b71fcb1495c7d299cc5e9741fa30) +Signed-off-by: Hugo SIMELIERE (Schneider Electric) <[email protected]> +--- + include/loopdev.h | 3 ++- + lib/loopdev.c | 7 ++++++- + libmount/src/hook_loopdev.c | 3 ++- + 3 files changed, 10 insertions(+), 3 deletions(-) + +diff --git a/include/loopdev.h b/include/loopdev.h +index 903adc491..d03e9b65e 100644 +--- a/include/loopdev.h ++++ b/include/loopdev.h +@@ -139,7 +139,8 @@ enum { + LOOPDEV_FL_NOIOCTL = (1 << 6), + LOOPDEV_FL_DEVSUBDIR = (1 << 7), + LOOPDEV_FL_CONTROL = (1 << 8), /* system with /dev/loop-control */ +- LOOPDEV_FL_SIZELIMIT = (1 << 9) ++ LOOPDEV_FL_SIZELIMIT = (1 << 9), ++ LOOPDEV_FL_NOFOLLOW = (1 << 10) /* O_NOFOLLOW, don't follow symlinks */ + }; + + /* +diff --git a/lib/loopdev.c b/lib/loopdev.c +index dd9ead3ee..4da251812 100644 +--- a/lib/loopdev.c ++++ b/lib/loopdev.c +@@ -1193,7 +1193,10 @@ int loopcxt_set_backing_file(struct loopdev_cxt *lc, const char *filename) + if (!lc) + return -EINVAL; + +- lc->filename = canonicalize_path(filename); ++ if (lc->flags & LOOPDEV_FL_NOFOLLOW) ++ lc->filename = strdup(filename); ++ else ++ lc->filename = canonicalize_path(filename); + if (!lc->filename) + return -errno; + +@@ -1332,6 +1335,8 @@ int loopcxt_setup_device(struct loopdev_cxt *lc) + + if (lc->config.info.lo_flags & LO_FLAGS_DIRECT_IO) + flags |= O_DIRECT; ++ if (lc->flags & LOOPDEV_FL_NOFOLLOW) ++ flags |= O_NOFOLLOW; + + if ((file_fd = open(lc->filename, mode | flags)) < 0) { + if (mode != O_RDONLY && (errno == EROFS || errno == EACCES)) +diff --git a/libmount/src/hook_loopdev.c b/libmount/src/hook_loopdev.c +index 8c8f7f218..ce39a7a70 100644 +--- a/libmount/src/hook_loopdev.c ++++ b/libmount/src/hook_loopdev.c +@@ -276,7 +276,8 @@ static int setup_loopdev(struct libmnt_context *cxt, + } + + DBG(LOOP, ul_debugobj(cxt, "not found; create a new loop device")); +- rc = loopcxt_init(&lc, 0); ++ rc = loopcxt_init(&lc, ++ mnt_context_is_restricted(cxt) ? LOOPDEV_FL_NOFOLLOW : 0); + if (rc) + goto done_no_deinit; + if (mnt_opt_has_value(loopopt)) { +-- +2.43.0 + -- 2.43.0
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