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author | Oleg Nesterov <oleg@redhat.com> | 2009-09-05 11:17:13 -0700 |
---|---|---|
committer | Linus Torvalds <torvalds@linux-foundation.org> | 2009-09-05 11:30:42 -0700 |
commit | a2a8474c3fff88d8dd52d05cb450563fb26fd26c (patch) | |
tree | 455415da039a77627f47ed19318bb9c8aa17de4d /fs/compat.c | |
parent | dd5d241ea955006122d76af88af87de73fec25b4 (diff) | |
download | kernel_samsung_tuna-a2a8474c3fff88d8dd52d05cb450563fb26fd26c.zip kernel_samsung_tuna-a2a8474c3fff88d8dd52d05cb450563fb26fd26c.tar.gz kernel_samsung_tuna-a2a8474c3fff88d8dd52d05cb450563fb26fd26c.tar.bz2 |
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.c | 17 |
1 files changed, 4 insertions, 13 deletions
diff --git a/fs/compat.c b/fs/compat.c index 94502da..6d6f98f 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(¤t->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(¤t->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(¤t->cred_guard_mutex); out_free: free_bprm(bprm); |