[Xen-changelog] [xen stable-4.4] libxc: check return values on mmap() and madvise() on xc_alloc_hypercall_buffer()

[patchbot@xxxxxxx]

commit b12283059bf07c7833f26552d45509b05ea83b30
Author:     Luis R. Rodriguez <mcgrof@xxxxxxxx>
AuthorDate: Tue May 20 05:37:35 2014 -0700
Commit:     Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
CommitDate: Mon Jan 12 15:39:37 2015 +0000

    libxc: check return values on mmap() and madvise() on 
xc_alloc_hypercall_buffer()
    
    On a Thinkpad T4440p with OpenSUSE tumbleweed with v3.15-rc4
    and today's latest xen tip from the git tree strace -f reveals
    we end up on a never ending wait shortly after
    
    write(20, "backend/console/5\0", 18 <unfinished ...>
    
    This is right before we just wait on the qemu process which we
    had mmap'd for. Without this you'll end up getting stuck on a
    loop if mmap() worked but madvise() did not. While at it I noticed
    even the mmap() error fail was not being checked, fix that too.
    
    Signed-off-by: Luis R. Rodriguez <mcgrof@xxxxxxxx>
    Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
    (cherry picked from commit e86539a388314cd3dca88f5e69d7873343197cd8)
---
 tools/libxc/xc_linux_osdep.c |   20 +++++++++++++++++++-
 1 files changed, 19 insertions(+), 1 deletions(-)

diff --git a/tools/libxc/xc_linux_osdep.c b/tools/libxc/xc_linux_osdep.c
index 73860a2..86bff3e 100644
--- a/tools/libxc/xc_linux_osdep.c
+++ b/tools/libxc/xc_linux_osdep.c
@@ -92,14 +92,32 @@ static void 
*linux_privcmd_alloc_hypercall_buffer(xc_interface *xch, xc_osdep_ha
 {
     size_t size = npages * XC_PAGE_SIZE;
     void *p;
+    int rc, saved_errno;
 
     /* Address returned by mmap is page aligned. */
     p = mmap(NULL, size, PROT_READ|PROT_WRITE, 
MAP_PRIVATE|MAP_ANONYMOUS|MAP_LOCKED, -1, 0);
+    if ( p == MAP_FAILED )
+    {
+        PERROR("xc_alloc_hypercall_buffer: mmap failed");
+        return NULL;
+    }
 
     /* Do not copy the VMA to child process on fork. Avoid the page being COW
         on hypercall. */
-    madvise(p, npages * XC_PAGE_SIZE, MADV_DONTFORK);
+    rc = madvise(p, npages * XC_PAGE_SIZE, MADV_DONTFORK);
+    if ( rc < 0 )
+    {
+        PERROR("xc_alloc_hypercall_buffer: madvise failed");
+        goto out;
+    }
+
     return p;
+
+out:
+    saved_errno = errno;
+    (void)munmap(p, size);
+    errno = saved_errno;
+    return NULL;
 }
 
 static void linux_privcmd_free_hypercall_buffer(xc_interface *xch, 
xc_osdep_handle h, void *ptr, int npages)
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.4

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