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authorOleg Nesterov <oleg@redhat.com>2009-09-05 22:17:13 +0400
committerLinus Torvalds <torvalds@linux-foundation.org>2009-09-05 22:30:42 +0400
commita2a8474c3fff88d8dd52d05cb450563fb26fd26c (patch)
tree455415da039a77627f47ed19318bb9c8aa17de4d /fs/compat.c
parentdd5d241ea955006122d76af88af87de73fec25b4 (diff)
downloadlinux-a2a8474c3fff88d8dd52d05cb450563fb26fd26c.tar.xz
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>
Diffstat (limited to 'fs/compat.c')
-rw-r--r--fs/compat.c17
1 files changed, 4 insertions, 13 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);