diff mbox series

[v2,2/6] linux-user: Fix MAP_FIXED_NOREPLACE on old kernels

Message ID 20230802071754.14876-3-akihiko.odaki@daynix.com
State New
Headers show
Series linux-user: brk/mmap fixes | expand

Commit Message

Akihiko Odaki Aug. 2, 2023, 7:17 a.m. UTC 
The man page states:
> Note that older kernels which do not recognize the MAP_FIXED_NOREPLACE
> flag will typically (upon detecting a collision with a preexisting
> mapping) fall back to a “non-MAP_FIXED” type of behavior: they will
> return an address that is different from the requested address.
> Therefore, backward-compatible software should check the returned
> address against the requested address.
https://man7.org/linux/man-pages/man2/mmap.2.html

Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
---
 linux-user/mmap.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)
diff mbox series

Patch

diff --git a/linux-user/mmap.c b/linux-user/mmap.c
index 14cd1b9feb..1a8477dbb2 100644
--- a/linux-user/mmap.c
+++ b/linux-user/mmap.c
@@ -263,7 +263,11 @@  static bool mmap_frag(abi_ulong real_start, abi_ulong start, abi_ulong last,
         void *p = mmap(host_start, qemu_host_page_size,
                        target_to_host_prot(prot),
                        flags | MAP_ANONYMOUS, -1, 0);
-        if (p == MAP_FAILED) {
+        if (p != host_start) {
+            if (p != MAP_FAILED) {
+                munmap(p, qemu_host_page_size);
+                errno = EEXIST;
+            }
             return false;
         }
         prot_old = prot;
@@ -686,7 +690,11 @@  abi_long target_mmap(abi_ulong start, abi_ulong len, int target_prot,
             }
             p = mmap(g2h_untagged(real_start), real_last - real_start + 1,
                      target_to_host_prot(target_prot), flags, fd, offset1);
-            if (p == MAP_FAILED) {
+            if (p != g2h_untagged(real_start)) {
+                if (p != MAP_FAILED) {
+                    munmap(p, real_last - real_start + 1);
+                    errno = EEXIST;
+                }
                 goto fail;
             }
             passthrough_start = real_start;