fs/coredump: prevent fsuid=0 dumps into user-controlled directories

[pandora-kernel.git] / fs / exec.c

diff --git a/fs/exec.c b/fs/exec.c
index 65785c9..a0006d8 100644 (file)
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -55,6 +55,9 @@
 #include <linux/pipe_fs_i.h>
 #include <linux/oom.h>
 #include <linux/compat.h>
+#include <linux/sched.h>
+#include <linux/fs.h>
+#include <linux/path.h>
 
 #include <asm/uaccess.h>
 #include <asm/mmu_context.h>
@@ -2134,9 +2137,9 @@ void do_coredump(long signr, int exit_code, struct pt_regs *regs)
        const struct cred *old_cred;
        struct cred *cred;
        int retval = 0;
-       int flag = 0;
        int ispipe;
-       bool need_nonrelative = false;
+       /* require nonrelative corefile path and be extra careful */
+       bool need_suid_safe = false;
        static atomic_t core_dump_count = ATOMIC_INIT(0);
        struct coredump_params cprm = {
                .signr = signr,
@@ -2169,9 +2172,8 @@ void do_coredump(long signr, int exit_code, struct pt_regs *regs)
         */
        if (__get_dumpable(cprm.mm_flags) == 2) {
                /* Setuid core dump mode */
-               flag = O_EXCL;          /* Stop rewrite attacks */
                cred->fsuid = 0;        /* Dump root private */
-               need_nonrelative = true;
+               need_suid_safe = true;
        }
 
        retval = coredump_wait(exit_code, &core_state);
@@ -2247,11 +2249,13 @@ void do_coredump(long signr, int exit_code, struct pt_regs *regs)
                }
        } else {
                struct inode *inode;
+               int open_flags = O_CREAT | O_RDWR | O_NOFOLLOW |
+                                O_LARGEFILE | O_EXCL;
 
                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);
@@ -2259,9 +2263,53 @@ void do_coredump(long signr, int exit_code, struct pt_regs *regs)
                        goto fail_unlock;
                }
 
-               cprm.file = filp_open(cn.corename,
-                                O_CREAT | 2 | O_NOFOLLOW | O_LARGEFILE | flag,
-                                0600);
+               /*
+                * 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.
+                */
+               if (need_suid_safe) {
+                       /*
+                        * Using user namespaces, normal user tasks can change
+                        * their current->fs->root to point to arbitrary
+                        * directories. Since the intention of the "only dump
+                        * with a fully qualified path" rule is to control where
+                        * coredumps may be placed using root privileges,
+                        * current->fs->root must not be used. Instead, use the
+                        * root directory of init_task.
+                        */
+                       struct path root;
+
+                       task_lock(&init_task);
+                       get_fs_root(init_task.fs, &root);
+                       task_unlock(&init_task);
+                       cprm.file = file_open_root(root.dentry, root.mnt,
+                               cn.corename, open_flags, 0600);
+                       path_put(&root);
+               } else {
+                       cprm.file = filp_open(cn.corename, open_flags, 0600);
+               }
                if (IS_ERR(cprm.file))
                        goto fail_unlock;