From 573a259336f8c57739bdaf035aa7abbae7d9a713 Mon Sep 17 00:00:00 2001
From: Axel Rasmussen <axelrasmussen@google.com>
Date: Sat, 5 Dec 2020 22:15:05 -0800
Subject: [PATCH] userfaultfd: selftests: fix SIGSEGV if huge mmap fails
The error handling in hugetlb_allocate_area() was incorrect for the
hugetlb_shared test case.
Previously the behavior was:
- mmap a hugetlb area
- If this fails, set the pointer to NULL, and carry on
- mmap an alias of the same hugetlb fd
- If this fails, munmap the original area
If the original mmap failed, it's likely the second one did too. If
both failed, we'd blindly try to munmap a NULL pointer, causing a
SIGSEGV. Instead, "goto fail" so we return before trying to mmap the
alias.
This issue can be hit "in real life" by forgetting to set
/proc/sys/vm/nr_hugepages (leaving it at 0), and then trying to run the
hugetlb_shared test.
Another small improvement is, when the original mmap fails, don't just
print "it failed": perror(), so we can see *why*. :)
Signed-off-by: Axel Rasmussen <axelrasmussen@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Peter Xu <peterx@redhat.com>
Cc: Joe Perches <joe@perches.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: David Alan Gilbert <dgilbert@redhat.com>
Link: https://lkml.kernel.org/r/20201204203443.2714693-1-axelrasmussen@google.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
tools/testing/selftests/vm/userfaultfd.c | 25 +++++++++++++++---------
1 file changed, 16 insertions(+), 9 deletions(-)
diff --git a/tools/testing/selftests/vm/userfaultfd.c b/tools/testing/selftests/vm/userfaultfd.c
index 9b0912a017777..c4425597769a0 100644
--- a/tools/testing/selftests/vm/userfaultfd.c
+++ b/tools/testing/selftests/vm/userfaultfd.c
@@ -206,19 +206,19 @@ static int hugetlb_release_pages(char *rel_area)
return ret;
}
-
static void hugetlb_allocate_area(void **alloc_area)
{
void *area_alias = NULL;
char **alloc_area_alias;
+
*alloc_area = mmap(NULL, nr_pages * page_size, PROT_READ | PROT_WRITE,
(map_shared ? MAP_SHARED : MAP_PRIVATE) |
MAP_HUGETLB,
huge_fd, *alloc_area == area_src ? 0 :
nr_pages * page_size);
if (*alloc_area == MAP_FAILED) {
- fprintf(stderr, "mmap of hugetlbfs file failed\n");
- *alloc_area = NULL;
+ perror("mmap of hugetlbfs file failed");
+ goto fail;
}
if (map_shared) {
@@ -227,14 +227,11 @@ static void hugetlb_allocate_area(void **alloc_area)
huge_fd, *alloc_area == area_src ? 0 :
nr_pages * page_size);
if (area_alias == MAP_FAILED) {
- if (munmap(*alloc_area, nr_pages * page_size) < 0) {
- perror("hugetlb munmap");
- exit(1);
- }
- *alloc_area = NULL;
- return;
+ perror("mmap of hugetlb file alias failed");
+ goto fail_munmap;
}
}
+
if (*alloc_area == area_src) {
huge_fd_off0 = *alloc_area;
alloc_area_alias = &area_src_alias;
@@ -243,6 +240,16 @@ static void hugetlb_allocate_area(void **alloc_area)
}
if (area_alias)
*alloc_area_alias = area_alias;
+
+ return;
+
+fail_munmap:
+ if (munmap(*alloc_area, nr_pages * page_size) < 0) {
+ perror("hugetlb munmap");
+ exit(1);
+ }
+fail:
+ *alloc_area = NULL;
}
static void hugetlb_alias_mapping(__u64 *start, size_t len, unsigned long offset)
--
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