[Devel] [PATCH RHEL7 COMMIT] ms/fs/proc/base.c: fix GPF in /proc/$PID/map_files

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-514.26.1.vz7.33.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-514.26.1.vz7.33.8
------>
commit 730f6e763886c63ec8657659c2a444b1839b0954
Author: Artem Fetishev <artem_fetishev at epam.com>
Date:   Mon Jul 17 18:43:53 2017 +0400

    ms/fs/proc/base.c: fix GPF in /proc/$PID/map_files
    
    The expected logic of proc_map_files_get_link() is either to return 0
    and initialize 'path' or return an error and leave 'path' uninitialized.
    
    By the time dname_to_vma_addr() returns 0 the corresponding vma may have
    already be gone.  In this case the path is not initialized but the
    return value is still 0.  This results in 'general protection fault'
    inside d_path().
    
    Steps to reproduce:
    
      CONFIG_CHECKPOINT_RESTORE=y
    
        fd = open(...);
        while (1) {
            mmap(fd, ...);
            munmap(fd, ...);
        }
    
      ls -la /proc/$PID/map_files
    
    Addresses https://bugzilla.kernel.org/show_bug.cgi?id=68991
    
    https://jira.sw.ru/browse/PSBM-68472
    
    Signed-off-by: Artem Fetishev <artem_fetishev at epam.com>
    Signed-off-by: Aleksandr Terekhov <aleksandr_terekhov at epam.com>
    Reported-by: <wiebittewas at gmail.com>
    Acked-by: Pavel Emelyanov <xemul at parallels.com>
    Acked-by: Cyrill Gorcunov <gorcunov at openvz.org>
    Reviewed-by: "Eric W. Biederman" <ebiederm at xmission.com>
    Cc: <stable at vger.kernel.org>
    Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
    
    ms commit: 70335ab ("fs/proc/base.c: fix GPF in /proc/$PID/map_files")
    
    Signed-off-by: Stanislav Kinsburskiy <skinsbursky at virtuozzo.com>
---
 fs/proc/base.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 0af670c..291e503 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -2028,6 +2028,7 @@ static int proc_map_files_get_link(struct dentry *dentry, struct path *path)
 	if (rc)
 		goto out_mmput;
 
+	rc = -ENOENT;
 	down_read(&mm->mmap_sem);
 	vma = find_exact_vma(mm, vm_start, vm_end);
 	if (vma && vma->vm_file) {