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From: | Jonathan Marler |
Subject: | Re: [PATCH] linux-user/mmap.c: fix integer underflow in target_mremap |
Date: | Sat, 2 May 2020 17:43:12 -0600 |
Fixes: https://bugs.launchpad.net/bugs/1876373
This code path in mmap occurs when a page size is decreased with mremap. When a section of pages is shrunk, qemu calls mmap_reserve on the pages that were released. However, it has the diff operation reversed, subtracting the larger old_size from the smaller new_size. Instead, it should be subtracting the smaller new_size from the larger old_size. You can also see in the previous line of the change that this mmap_reserve call only occurs when old_size > new_size.
Signed-off-by: Jonathan Marler <address@hidden>
---
linux-user/mmap.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/linux-user/mmap.c b/linux-user/mmap.c
index e378033797..caab62909e 100644
--- a/linux-user/mmap.c
+++ b/linux-user/mmap.c
@@ -708,7 +708,7 @@ abi_long target_mremap(abi_ulong old_addr, abi_ulong old_size,
if (prot == 0) {
host_addr = mremap(g2h(old_addr), old_size, new_size, flags);
if (host_addr != MAP_FAILED && reserved_va && old_size > new_size) {
- mmap_reserve(old_addr + old_size, new_size - old_size);
+ mmap_reserve(old_addr + old_size, old_size - new_size);
}
} else {
errno = ENOMEM;
--
2.23.1
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