From: Cyrill Gorcunov Date: Fri, 18 May 2012 00:03:25 +0000 (-0700) Subject: fs, proc: fix ABBA deadlock in case of execution attempt of map_files/ entries X-Git-Url: http://git.alex.org.uk fs, proc: fix ABBA deadlock in case of execution attempt of map_files/ entries map_files/ entries are never supposed to be executed, still curious minds might try to run them, which leads to the following deadlock ====================================================== [ INFO: possible circular locking dependency detected ] 3.4.0-rc4-24406-g841e6a6 #121 Not tainted ------------------------------------------------------- bash/1556 is trying to acquire lock: (&sb->s_type->i_mutex_key#8){+.+.+.}, at: do_lookup+0x267/0x2b1 but task is already holding lock: (&sig->cred_guard_mutex){+.+.+.}, at: prepare_bprm_creds+0x2d/0x69 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #1 (&sig->cred_guard_mutex){+.+.+.}: validate_chain+0x444/0x4f4 __lock_acquire+0x387/0x3f8 lock_acquire+0x12b/0x158 __mutex_lock_common+0x56/0x3a9 mutex_lock_killable_nested+0x40/0x45 lock_trace+0x24/0x59 proc_map_files_lookup+0x5a/0x165 __lookup_hash+0x52/0x73 do_lookup+0x276/0x2b1 walk_component+0x3d/0x114 do_last+0xfc/0x540 path_openat+0xd3/0x306 do_filp_open+0x3d/0x89 do_sys_open+0x74/0x106 sys_open+0x21/0x23 tracesys+0xdd/0xe2 -> #0 (&sb->s_type->i_mutex_key#8){+.+.+.}: check_prev_add+0x6a/0x1ef validate_chain+0x444/0x4f4 __lock_acquire+0x387/0x3f8 lock_acquire+0x12b/0x158 __mutex_lock_common+0x56/0x3a9 mutex_lock_nested+0x40/0x45 do_lookup+0x267/0x2b1 walk_component+0x3d/0x114 link_path_walk+0x1f9/0x48f path_openat+0xb6/0x306 do_filp_open+0x3d/0x89 open_exec+0x25/0xa0 do_execve_common+0xea/0x2f9 do_execve+0x43/0x45 sys_execve+0x43/0x5a stub_execve+0x6c/0xc0 This is because prepare_bprm_creds grabs task->signal->cred_guard_mutex and when do_lookup happens we try to grab task->signal->cred_guard_mutex again in lock_trace. Fix it using plain ptrace_may_access() helper in proc_map_files_lookup() and in proc_map_files_readdir() instead of lock_trace(), the caller must be CAP_SYS_ADMIN granted anyway. Signed-off-by: Cyrill Gorcunov Reported-by: Sasha Levin Cc: Konstantin Khlebnikov Cc: Pavel Emelyanov Cc: Dave Jones Cc: Vasiliy Kulikov Cc: Oleg Nesterov Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/fs/proc/base.c b/fs/proc/base.c index 1c8b280..8e139c9 100644 --- a/fs/proc/base.c +++ b/fs/proc/base.c @@ -2177,16 +2177,16 @@ static struct dentry *proc_map_files_lookup(struct inode *dir, goto out; result = ERR_PTR(-EACCES); - if (lock_trace(task)) + if (!ptrace_may_access(task, PTRACE_MODE_READ)) goto out_put_task; result = ERR_PTR(-ENOENT); if (dname_to_vma_addr(dentry, &vm_start, &vm_end)) - goto out_unlock; + goto out_put_task; mm = get_task_mm(task); if (!mm) - goto out_unlock; + goto out_put_task; down_read(&mm->mmap_sem); vma = find_exact_vma(mm, vm_start, vm_end); @@ -2198,8 +2198,6 @@ static struct dentry *proc_map_files_lookup(struct inode *dir, out_no_vma: up_read(&mm->mmap_sem); mmput(mm); -out_unlock: - unlock_trace(task); out_put_task: put_task_struct(task); out: @@ -2233,7 +2231,7 @@ proc_map_files_readdir(struct file *filp, void *dirent, filldir_t filldir) goto out; ret = -EACCES; - if (lock_trace(task)) + if (!ptrace_may_access(task, PTRACE_MODE_READ)) goto out_put_task; ret = 0; @@ -2241,12 +2239,12 @@ proc_map_files_readdir(struct file *filp, void *dirent, filldir_t filldir) case 0: ino = inode->i_ino; if (filldir(dirent, ".", 1, 0, ino, DT_DIR) < 0) - goto out_unlock; + goto out_put_task; filp->f_pos++; case 1: ino = parent_ino(dentry); if (filldir(dirent, "..", 2, 1, ino, DT_DIR) < 0) - goto out_unlock; + goto out_put_task; filp->f_pos++; default: { @@ -2257,7 +2255,7 @@ proc_map_files_readdir(struct file *filp, void *dirent, filldir_t filldir) mm = get_task_mm(task); if (!mm) - goto out_unlock; + goto out_put_task; down_read(&mm->mmap_sem); nr_files = 0; @@ -2287,7 +2285,7 @@ proc_map_files_readdir(struct file *filp, void *dirent, filldir_t filldir) flex_array_free(fa); up_read(&mm->mmap_sem); mmput(mm); - goto out_unlock; + goto out_put_task; } for (i = 0, vma = mm->mmap, pos = 2; vma; vma = vma->vm_next) { @@ -2332,8 +2330,6 @@ proc_map_files_readdir(struct file *filp, void *dirent, filldir_t filldir) } } -out_unlock: - unlock_trace(task); out_put_task: put_task_struct(task); out: