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authorOleg Nesterov <oleg@redhat.com>2009-09-05 11:17:13 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2009-09-05 11:30:42 -0700
commita2a8474c3fff88d8dd52d05cb450563fb26fd26c (patch)
tree455415da039a77627f47ed19318bb9c8aa17de4d
parentdd5d241ea955006122d76af88af87de73fec25b4 (diff)
exec: do not sleep in TASK_TRACED under ->cred_guard_mutex
Tom Horsley reports that his debugger hangs when it tries to read /proc/pid_of_tracee/maps, this happens since "mm_for_maps: take ->cred_guard_mutex to fix the race with exec" 04b836cbf19e885f8366bccb2e4b0474346c02d commit in 2.6.31. But the root of the problem lies in the fact that do_execve() path calls tracehook_report_exec() which can stop if the tracer sets PT_TRACE_EXEC. The tracee must not sleep in TASK_TRACED holding this mutex. Even if we remove ->cred_guard_mutex from mm_for_maps() and proc_pid_attr_write(), another task doing PTRACE_ATTACH should not hang until it is killed or the tracee resumes. With this patch do_execve() does not use ->cred_guard_mutex directly and we do not hold it throughout, instead: - introduce prepare_bprm_creds() helper, it locks the mutex and calls prepare_exec_creds() to initialize bprm->cred. - install_exec_creds() drops the mutex after commit_creds(), and thus before tracehook_report_exec()->ptrace_stop(). or, if exec fails, free_bprm() drops this mutex when bprm->cred != NULL which indicates install_exec_creds() was not called. Reported-by: Tom Horsley <tom.horsley@att.net> Signed-off-by: Oleg Nesterov <oleg@redhat.com> Acked-by: David Howells <dhowells@redhat.com> Cc: Roland McGrath <roland@redhat.com> Cc: James Morris <jmorris@namei.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--fs/compat.c17
-rw-r--r--fs/exec.c63
-rw-r--r--include/linux/binfmts.h1
3 files changed, 43 insertions, 38 deletions
diff --git a/fs/compat.c b/fs/compat.c
index 94502dab972a..6d6f98fe64a0 100644
--- a/fs/compat.c
+++ b/fs/compat.c
@@ -1485,20 +1485,15 @@ int compat_do_execve(char * filename,
if (!bprm)
goto out_files;
- retval = -ERESTARTNOINTR;
- if (mutex_lock_interruptible(&current->cred_guard_mutex))
+ retval = prepare_bprm_creds(bprm);
+ if (retval)
goto out_free;
- current->in_execve = 1;
-
- retval = -ENOMEM;
- bprm->cred = prepare_exec_creds();
- if (!bprm->cred)
- goto out_unlock;
retval = check_unsafe_exec(bprm);
if (retval < 0)
- goto out_unlock;
+ goto out_free;
clear_in_exec = retval;
+ current->in_execve = 1;
file = open_exec(filename);
retval = PTR_ERR(file);
@@ -1547,7 +1542,6 @@ int compat_do_execve(char * filename,
/* execve succeeded */
current->fs->in_exec = 0;
current->in_execve = 0;
- mutex_unlock(&current->cred_guard_mutex);
acct_update_integrals(current);
free_bprm(bprm);
if (displaced)
@@ -1567,10 +1561,7 @@ out_file:
out_unmark:
if (clear_in_exec)
current->fs->in_exec = 0;
-
-out_unlock:
current->in_execve = 0;
- mutex_unlock(&current->cred_guard_mutex);
out_free:
free_bprm(bprm);
diff --git a/fs/exec.c b/fs/exec.c
index fb4f3cdda78c..172ceb6edde4 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1016,6 +1016,35 @@ out:
EXPORT_SYMBOL(flush_old_exec);
/*
+ * Prepare credentials and lock ->cred_guard_mutex.
+ * install_exec_creds() commits the new creds and drops the lock.
+ * Or, if exec fails before, free_bprm() should release ->cred and
+ * and unlock.
+ */
+int prepare_bprm_creds(struct linux_binprm *bprm)
+{
+ if (mutex_lock_interruptible(&current->cred_guard_mutex))
+ return -ERESTARTNOINTR;
+
+ bprm->cred = prepare_exec_creds();
+ if (likely(bprm->cred))
+ return 0;
+
+ mutex_unlock(&current->cred_guard_mutex);
+ return -ENOMEM;
+}
+
+void free_bprm(struct linux_binprm *bprm)
+{
+ free_arg_pages(bprm);
+ if (bprm->cred) {
+ mutex_unlock(&current->cred_guard_mutex);
+ abort_creds(bprm->cred);
+ }
+ kfree(bprm);
+}
+
+/*
* install the new credentials for this executable
*/
void install_exec_creds(struct linux_binprm *bprm)
@@ -1024,12 +1053,13 @@ void install_exec_creds(struct linux_binprm *bprm)
commit_creds(bprm->cred);
bprm->cred = NULL;
-
- /* cred_guard_mutex must be held at least to this point to prevent
+ /*
+ * cred_guard_mutex must be held at least to this point to prevent
* ptrace_attach() from altering our determination of the task's
- * credentials; any time after this it may be unlocked */
-
+ * credentials; any time after this it may be unlocked.
+ */
security_bprm_committed_creds(bprm);
+ mutex_unlock(&current->cred_guard_mutex);
}
EXPORT_SYMBOL(install_exec_creds);
@@ -1246,14 +1276,6 @@ int search_binary_handler(struct linux_binprm *bprm,struct pt_regs *regs)
EXPORT_SYMBOL(search_binary_handler);
-void free_bprm(struct linux_binprm *bprm)
-{
- free_arg_pages(bprm);
- if (bprm->cred)
- abort_creds(bprm->cred);
- kfree(bprm);
-}
-
/*
* sys_execve() executes a new program.
*/
@@ -1277,20 +1299,15 @@ int do_execve(char * filename,
if (!bprm)
goto out_files;
- retval = -ERESTARTNOINTR;
- if (mutex_lock_interruptible(&current->cred_guard_mutex))
+ retval = prepare_bprm_creds(bprm);
+ if (retval)
goto out_free;
- current->in_execve = 1;
-
- retval = -ENOMEM;
- bprm->cred = prepare_exec_creds();
- if (!bprm->cred)
- goto out_unlock;
retval = check_unsafe_exec(bprm);
if (retval < 0)
- goto out_unlock;
+ goto out_free;
clear_in_exec = retval;
+ current->in_execve = 1;
file = open_exec(filename);
retval = PTR_ERR(file);
@@ -1340,7 +1357,6 @@ int do_execve(char * filename,
/* execve succeeded */
current->fs->in_exec = 0;
current->in_execve = 0;
- mutex_unlock(&current->cred_guard_mutex);
acct_update_integrals(current);
free_bprm(bprm);
if (displaced)
@@ -1360,10 +1376,7 @@ out_file:
out_unmark:
if (clear_in_exec)
current->fs->in_exec = 0;
-
-out_unlock:
current->in_execve = 0;
- mutex_unlock(&current->cred_guard_mutex);
out_free:
free_bprm(bprm);
diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h
index 61ee18c1bdb4..2046b5b8af48 100644
--- a/include/linux/binfmts.h
+++ b/include/linux/binfmts.h
@@ -117,6 +117,7 @@ extern int setup_arg_pages(struct linux_binprm * bprm,
int executable_stack);
extern int bprm_mm_init(struct linux_binprm *bprm);
extern int copy_strings_kernel(int argc,char ** argv,struct linux_binprm *bprm);
+extern int prepare_bprm_creds(struct linux_binprm *bprm);
extern void install_exec_creds(struct linux_binprm *bprm);
extern void do_coredump(long signr, int exit_code, struct pt_regs *regs);
extern int set_binfmt(struct linux_binfmt *new);