From: Christian Brauner <brauner@kernel.org> stable inclusion from stable-v6.6.151 commit 1819f82dee766c58295ecaacdac02cdf6837d7a4 category: bugfix bugzilla: https://atomgit.com/src-openeuler/kernel/issues/17790 CVE: CVE-2026-74485 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=... ---------------------------------------------------------------------- commit 8e85d50ba1117fd446bf9a250bd8a97d48384bdc upstream. The registration string starts with a user chosen delimiter that separates the individual fields. So that the field parsers terminate even on a truncated string create_entry() pads the buffer with that same delimiter: memset(buf + count, del, 8); Most fields are scanned for the delimiter with strchr()/scanarg() and happily stop on the padding. The flags field is different: instead of scanning for the delimiter check_special_flags() consumes the flag characters 'P', 'O', 'C' and 'F' and stops at the first byte that is none of them, relying on the trailing delimiter to end the scan. If the delimiter is itself a flag character the padding no longer acts as a terminator. The scan swallows all eight padding bytes and keeps reading past the end of the allocation until it hits a byte that is not a flag character. For example registering PaPEPPxPPiP with 'P' as the delimiter (name "a", type extension, magic "x", interpreter "i", empty flags) leaves the flag scan running off the end of the buffer. The registration is rejected in the end because the parser does not stop exactly at buf + count, but only after the out of bounds read has already happened. With an unlucky allocation layout the scan can walk into an unmapped page; under KASAN it is reported as a slab out of bounds read. binfmt_misc mounts are available to unprivileged users in a user namespace so the read is reachable without privileges. Reject a delimiter that is one of the flag characters up front. Such a registration was always rejected anyway, only after the out of bounds read, so no valid registration string changes meaning. Link: https://patch.msgid.link/20260710-work-binfmt_misc-locking-v3-3-a162f7cb58d6... Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Cc: stable@vger.kernel.org Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Luo Gengkun <luogengkun2@huawei.com> --- fs/binfmt_misc.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/fs/binfmt_misc.c b/fs/binfmt_misc.c index bf954bac70a9..5f6e354cb565 100644 --- a/fs/binfmt_misc.c +++ b/fs/binfmt_misc.c @@ -349,6 +349,10 @@ static Node *create_entry(const char __user *buffer, size_t count) pr_debug("register: delim: %#x {%c}\n", del, del); + /* A flag-char delimiter runs the flag scan off the buffer. */ + if (del == 'P' || del == 'O' || del == 'C' || del == 'F') + goto einval; + /* Pad the buffer with the delim to simplify parsing below. */ memset(buf + count, del, 8); -- 2.34.1