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[31.0.3.137]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-a7acab4dec6sm890783066b.61.2024.08.01.05.08.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 01 Aug 2024 05:08:23 -0700 (PDT) From: =?utf-8?q?Wojciech_G=C5=82adysz?= To: viro@zeniv.linux.org.uk, brauner@kernel.org, jack@suse.cz, ebiederm@xmission.com, kees@kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: =?utf-8?q?Wojciech_G=C5=82adysz?= Subject: [PATCH] kernel/fs: last check for exec credentials on NOEXEC mount Date: Thu, 1 Aug 2024 14:07:45 +0200 Message-Id: <20240801120745.13318-1-wojciech.gladysz@infogain.com> X-Mailer: git-send-email 2.35.3 Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Test case: thread mounts NOEXEC fuse to a file being executed. WARN_ON_ONCE is triggered yielding panic for some config. Add a check to security_bprm_creds_for_exec(bprm). Stack trace: ------------[ cut here ]------------ WARNING: CPU: 0 PID: 2736 at fs/exec.c:933 do_open_execat+0x311/0x710 fs/exec.c:932 Modules linked in: CPU: 0 PID: 2736 Comm: syz-executor384 Not tainted 5.10.0-syzkaller #0 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014 RIP: 0010:do_open_execat+0x311/0x710 fs/exec.c:932 Code: 89 de e8 02 b1 a1 ff 31 ff 89 de e8 f9 b0 a1 ff 45 84 ff 75 2e 45 85 ed 0f 8f ed 03 00 00 e8 56 ae a1 ff eb bd e8 4f ae a1 ff <0f> 0b 48 c7 c3 f3 ff ff ff 4c 89 f7 e8 9e cb fe ff 49 89 de e9 2d RSP: 0018:ffffc90008e07c20 EFLAGS: 00010293 RAX: ffffffff82131ac6 RBX: 0000000000000004 RCX: ffff88801a6611c0 RDX: 0000000000000000 RSI: 0000000000000004 RDI: 0000000000000000 RBP: ffffc90008e07cf0 R08: ffffffff8213173f R09: ffffc90008e07aa0 R10: 0000000000000000 R11: dffffc0000000001 R12: ffff8880115810e0 R13: dffffc0000000000 R14: ffff88801122c040 R15: ffffc90008e07c60 FS: 00007f9e283ce6c0(0000) GS:ffff888058a00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f9e2848600a CR3: 00000000139de000 CR4: 0000000000352ef0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: bprm_execve+0x60b/0x1c40 fs/exec.c:1939 do_execveat_common+0x5a6/0x770 fs/exec.c:2077 do_execve fs/exec.c:2147 [inline] __do_sys_execve fs/exec.c:2223 [inline] __se_sys_execve fs/exec.c:2218 [inline] __x64_sys_execve+0x92/0xb0 fs/exec.c:2218 do_syscall_64+0x6d/0xa0 arch/x86/entry/common.c:62 entry_SYSCALL_64_after_hwframe+0x61/0xcb RIP: 0033:0x7f9e2842f299 Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 b1 18 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b0 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007f9e283ce218 EFLAGS: 00000246 ORIG_RAX: 000000000000003b RAX: ffffffffffffffda RBX: 00007f9e284bd3f8 RCX: 00007f9e2842f299 RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000020000400 RBP: 00007f9e284bd3f0 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 00007f9e2848a134 R13: 0030656c69662f2e R14: 00007ffc819a23d0 R15: 00007f9e28488130 Signed-off-by: Wojciech Gładysz --- fs/exec.c | 42 +++++++++++++++++++----------------------- 1 file changed, 19 insertions(+), 23 deletions(-) diff --git a/fs/exec.c b/fs/exec.c index a126e3d1cacb..0cc6a7d033a1 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -953,8 +953,6 @@ EXPORT_SYMBOL(transfer_args_to_stack); */ static struct file *do_open_execat(int fd, struct filename *name, int flags) { - struct file *file; - int err; struct open_flags open_exec_flags = { .open_flag = O_LARGEFILE | O_RDONLY | __FMODE_EXEC, .acc_mode = MAY_EXEC, @@ -969,26 +967,7 @@ static struct file *do_open_execat(int fd, struct filename *name, int flags) if (flags & AT_EMPTY_PATH) open_exec_flags.lookup_flags |= LOOKUP_EMPTY; - file = do_filp_open(fd, name, &open_exec_flags); - if (IS_ERR(file)) - goto out; - - /* - * may_open() has already checked for this, so it should be - * impossible to trip now. But we need to be extra cautious - * and check again at the very end too. - */ - err = -EACCES; - if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode) || - path_noexec(&file->f_path))) - goto exit; - -out: - return file; - -exit: - fput(file); - return ERR_PTR(err); + return do_filp_open(fd, name, &open_exec_flags); } /** @@ -1730,6 +1709,23 @@ static void bprm_fill_uid(struct linux_binprm *bprm, struct file *file) } } +static int bprm_creds_for_exec(struct linux_binprm *bprm) +{ + struct file *file = bprm->file; + + /* + * Do not execute a regular file on NOEXEC mount. + * May_open() has already checked for this but a NOEXEC mount + * operation may have happened to the file since then (fuse). + * This is the last check point. + */ + if (!S_ISREG(file_inode(file)->i_mode) || + path_noexec(&file->f_path)) + return -EACCES; + + return security_bprm_creds_for_exec(bprm); +} + /* * Compute brpm->cred based upon the final binary. */ @@ -1907,7 +1903,7 @@ static int bprm_execve(struct linux_binprm *bprm) sched_exec(); /* Set the unchanging part of bprm->cred */ - retval = security_bprm_creds_for_exec(bprm); + retval = bprm_creds_for_exec(bprm); if (retval) goto out;