Merge tag 'v3.10.90' into update

[GitHub/mt8127/android_kernel_alcatel_ttab.git] / fs / coredump.c

diff --git a/fs/coredump.c b/fs/coredump.c
index 3ef964b5c03de30a8b9c2968464d3e87d1756ace..81c862591ca1da42885fab5f686fcad531c3c9e2 100644 (file)
--- a/fs/coredump.c
+++ b/fs/coredump.c
@@ -491,10 +491,10 @@ void do_coredump(siginfo_t *siginfo)
        const struct cred *old_cred;
        struct cred *cred;
        int retval = 0;
-       int flag = 0;
        int ispipe;
        struct files_struct *displaced;
-       bool need_nonrelative = false;
+       /* require nonrelative corefile path and be extra careful */
+       bool need_suid_safe = false;
        bool core_dumped = false;
        static atomic_t core_dump_count = ATOMIC_INIT(0);
        struct coredump_params cprm = {
@@ -537,9 +537,8 @@ void do_coredump(siginfo_t *siginfo)
         */
        if (__get_dumpable(cprm.mm_flags) == SUID_DUMP_ROOT) {
                /* Setuid core dump mode */
-               flag = O_EXCL;          /* Stop rewrite attacks */
                cred->fsuid = GLOBAL_ROOT_UID;  /* Dump root private */
-               need_nonrelative = true;
+               need_suid_safe = true;
        }
 
        retval = coredump_wait(siginfo->si_signo, &core_state);
@@ -620,7 +619,7 @@ void do_coredump(siginfo_t *siginfo)
                if (cprm.limit < binfmt->min_coredump)
                        goto fail_unlock;
 
-               if (need_nonrelative && cn.corename[0] != '/') {
+               if (need_suid_safe && cn.corename[0] != '/') {
                        printk(KERN_WARNING "Pid %d(%s) can only dump core "\
                                "to fully qualified path!\n",
                                task_tgid_vnr(current), current->comm);
@@ -628,8 +627,35 @@ void do_coredump(siginfo_t *siginfo)
                        goto fail_unlock;
                }
 
+               /*
+                * Unlink the file if it exists unless this is a SUID
+                * binary - in that case, we're running around with root
+                * privs and don't want to unlink another user's coredump.
+                */
+               if (!need_suid_safe) {
+                       mm_segment_t old_fs;
+
+                       old_fs = get_fs();
+                       set_fs(KERNEL_DS);
+                       /*
+                        * If it doesn't exist, that's fine. If there's some
+                        * other problem, we'll catch it at the filp_open().
+                        */
+                       (void) sys_unlink((const char __user *)cn.corename);
+                       set_fs(old_fs);
+               }
+
+               /*
+                * There is a race between unlinking and creating the
+                * file, but if that causes an EEXIST here, that's
+                * fine - another process raced with us while creating
+                * the corefile, and the other process won. To userspace,
+                * what matters is that at least one of the two processes
+                * writes its coredump successfully, not which one.
+                */
                cprm.file = filp_open(cn.corename,
-                                O_CREAT | 2 | O_NOFOLLOW | O_LARGEFILE | flag,
+                                O_CREAT | 2 | O_NOFOLLOW |
+                                O_LARGEFILE | O_EXCL,
                                 0600);
                if (IS_ERR(cprm.file))
                        goto fail_unlock;