From 8c652f96d3852b97a49c331cd0bb02d22f3cb31b Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Fri, 24 Apr 2009 01:01:56 +0200 Subject: do_execve() must not clear fs->in_exec if it was set by another thread If do_execve() fails after check_unsafe_exec(), it clears fs->in_exec unconditionally. This is wrong if we race with our sub-thread which also does do_execve: Two threads T1 and T2 and another process P, all share the same ->fs. T1 starts do_execve(BAD_FILE). It calls check_unsafe_exec(), since ->fs is shared, we set LSM_UNSAFE but not ->in_exec. P exits and decrements fs->users. T2 starts do_execve(), calls check_unsafe_exec(), now ->fs is not shared, we set fs->in_exec. T1 continues, open_exec(BAD_FILE) fails, we clear ->in_exec and return to the user-space. T1 does clone(CLONE_FS /* without CLONE_THREAD */). T2 continues without LSM_UNSAFE_SHARE while ->fs is shared with another process. Change check_unsafe_exec() to return res = 1 if we set ->in_exec, and change do_execve() to clear ->in_exec depending on res. When do_execve() suceeds, it is safe to clear ->in_exec unconditionally. It can be set only if we don't share ->fs with another process, and since we already killed all sub-threads either ->in_exec == 0 or we are the only user of this ->fs. Also, we do not need fs->lock to clear fs->in_exec. Signed-off-by: Oleg Nesterov Acked-by: Roland McGrath Acked-by: Hugh Dickins Signed-off-by: Linus Torvalds --- fs/compat.c | 11 +++++------ 1 file changed, 5 insertions(+), 6 deletions(-) (limited to 'fs/compat.c') diff --git a/fs/compat.c b/fs/compat.c index 379a399..681ed81 100644 --- a/fs/compat.c +++ b/fs/compat.c @@ -1476,6 +1476,7 @@ int compat_do_execve(char * filename, struct linux_binprm *bprm; struct file *file; struct files_struct *displaced; + bool clear_in_exec; int retval; retval = unshare_files(&displaced); @@ -1498,8 +1499,9 @@ int compat_do_execve(char * filename, goto out_unlock; retval = check_unsafe_exec(bprm); - if (retval) + if (retval < 0) goto out_unlock; + clear_in_exec = retval; file = open_exec(filename); retval = PTR_ERR(file); @@ -1546,9 +1548,7 @@ int compat_do_execve(char * filename, goto out; /* execve succeeded */ - write_lock(¤t->fs->lock); current->fs->in_exec = 0; - write_unlock(¤t->fs->lock); current->in_execve = 0; mutex_unlock(¤t->cred_exec_mutex); acct_update_integrals(current); @@ -1568,9 +1568,8 @@ out_file: } out_unmark: - write_lock(¤t->fs->lock); - current->fs->in_exec = 0; - write_unlock(¤t->fs->lock); + if (clear_in_exec) + current->fs->in_exec = 0; out_unlock: current->in_execve = 0; -- cgit v1.1