path: root/fs
diff options
authorDavid Howells <dhowells@redhat.com>2009-02-06 11:45:46 +0000
committerJames Morris <jmorris@namei.org>2009-02-07 08:46:18 +1100
commit0bf2f3aec5474da80a60e1baca629af87ecb67b6 (patch)
tree5c1a7733e24aaacbcf46e0434a11f033cfde43ca /fs
parent6cec50838ed04a9833fb5549f698d3756bbe7e72 (diff)
CRED: Fix SUID exec regression
The patch: commit a6f76f23d297f70e2a6b3ec607f7aeeea9e37e8d CRED: Make execve() take advantage of copy-on-write credentials moved the place in which the 'safeness' of a SUID/SGID exec was performed to before de_thread() was called. This means that LSM_UNSAFE_SHARE is now calculated incorrectly. This flag is set if any of the usage counts for fs_struct, files_struct and sighand_struct are greater than 1 at the time the determination is made. All of which are true for threads created by the pthread library. However, since we wish to make the security calculation before irrevocably damaging the process so that we can return it an error code in the case where we decide we want to reject the exec request on this basis, we have to make the determination before calling de_thread(). So, instead, we count up the number of threads (CLONE_THREAD) that are sharing our fs_struct (CLONE_FS), files_struct (CLONE_FILES) and sighand_structs (CLONE_SIGHAND/CLONE_THREAD) with us. These will be killed by de_thread() and so can be discounted by check_unsafe_exec(). We do have to be careful because CLONE_THREAD does not imply FS or FILES. We _assume_ that there will be no extra references to these structs held by the threads we're going to kill. This can be tested with the attached pair of programs. Build the two programs using the Makefile supplied, and run ./test1 as a non-root user. If successful, you should see something like: [dhowells@andromeda tmp]$ ./test1 --TEST1-- uid=4043, euid=4043 suid=4043 exec ./test2 --TEST2-- uid=4043, euid=0 suid=0 SUCCESS - Correct effective user ID and if unsuccessful, something like: [dhowells@andromeda tmp]$ ./test1 --TEST1-- uid=4043, euid=4043 suid=4043 exec ./test2 --TEST2-- uid=4043, euid=4043 suid=4043 ERROR - Incorrect effective user ID! The non-root user ID you see will depend on the user you run as. [test1.c] #include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <pthread.h> static void *thread_func(void *arg) { while (1) {} } int main(int argc, char **argv) { pthread_t tid; uid_t uid, euid, suid; printf("--TEST1--\n"); getresuid(&uid, &euid, &suid); printf("uid=%d, euid=%d suid=%d\n", uid, euid, suid); if (pthread_create(&tid, NULL, thread_func, NULL) < 0) { perror("pthread_create"); exit(1); } printf("exec ./test2\n"); execlp("./test2", "test2", NULL); perror("./test2"); _exit(1); } [test2.c] #include <stdio.h> #include <stdlib.h> #include <unistd.h> int main(int argc, char **argv) { uid_t uid, euid, suid; getresuid(&uid, &euid, &suid); printf("--TEST2--\n"); printf("uid=%d, euid=%d suid=%d\n", uid, euid, suid); if (euid != 0) { fprintf(stderr, "ERROR - Incorrect effective user ID!\n"); exit(1); } printf("SUCCESS - Correct effective user ID\n"); exit(0); } [Makefile] CFLAGS = -D_GNU_SOURCE -Wall -Werror -Wunused all: test1 test2 test1: test1.c gcc $(CFLAGS) -o test1 test1.c -lpthread test2: test2.c gcc $(CFLAGS) -o test2 test2.c sudo chown root.root test2 sudo chmod +s test2 Reported-by: David Smith <dsmith@redhat.com> Signed-off-by: David Howells <dhowells@redhat.com> Acked-by: David Smith <dsmith@redhat.com> Signed-off-by: James Morris <jmorris@namei.org>
Diffstat (limited to 'fs')
3 files changed, 24 insertions, 8 deletions
diff --git a/fs/compat.c b/fs/compat.c
index 65a070e705a..d0145ca2757 100644
--- a/fs/compat.c
+++ b/fs/compat.c
@@ -1407,7 +1407,7 @@ int compat_do_execve(char * filename,
bprm->cred = prepare_exec_creds();
if (!bprm->cred)
goto out_unlock;
- check_unsafe_exec(bprm);
+ check_unsafe_exec(bprm, current->files);
file = open_exec(filename);
retval = PTR_ERR(file);
diff --git a/fs/exec.c b/fs/exec.c
index 0dd60a01f1b..929b58004b7 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1049,16 +1049,32 @@ EXPORT_SYMBOL(install_exec_creds);
* - the caller must hold current->cred_exec_mutex to protect against
-void check_unsafe_exec(struct linux_binprm *bprm)
+void check_unsafe_exec(struct linux_binprm *bprm, struct files_struct *files)
- struct task_struct *p = current;
+ struct task_struct *p = current, *t;
+ unsigned long flags;
+ unsigned n_fs, n_files, n_sighand;
bprm->unsafe = tracehook_unsafe_exec(p);
- if (atomic_read(&p->fs->count) > 1 ||
- atomic_read(&p->files->count) > 1 ||
- atomic_read(&p->sighand->count) > 1)
+ n_fs = 1;
+ n_files = 1;
+ n_sighand = 1;
+ lock_task_sighand(p, &flags);
+ for (t = next_thread(p); t != p; t = next_thread(t)) {
+ if (t->fs == p->fs)
+ n_fs++;
+ if (t->files == files)
+ n_files++;
+ n_sighand++;
+ }
+ if (atomic_read(&p->fs->count) > n_fs ||
+ atomic_read(&p->files->count) > n_files ||
+ atomic_read(&p->sighand->count) > n_sighand)
bprm->unsafe |= LSM_UNSAFE_SHARE;
+ unlock_task_sighand(p, &flags);
@@ -1273,7 +1289,7 @@ int do_execve(char * filename,
bprm->cred = prepare_exec_creds();
if (!bprm->cred)
goto out_unlock;
- check_unsafe_exec(bprm);
+ check_unsafe_exec(bprm, displaced);
file = open_exec(filename);
retval = PTR_ERR(file);
diff --git a/fs/internal.h b/fs/internal.h
index 53af885f173..0d8ac497b3d 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -43,7 +43,7 @@ extern void __init chrdev_init(void);
* exec.c
-extern void check_unsafe_exec(struct linux_binprm *);
+extern void check_unsafe_exec(struct linux_binprm *, struct files_struct *);
* namespace.c