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authorPeter Maydell <peter.maydell@linaro.org>2018-04-19 13:11:09 +0100
committerPeter Maydell <peter.maydell@linaro.org>2018-04-19 13:11:09 +0100
commitbdea7dffd0afb0b4b18ad1b1ec8055771ccf93e1 (patch)
tree238622beef6ad3c436c98da3714fce9f50ecbf35
parent1b2503fcf7b5932c5a3779ca2ceb92bd403c4ee7 (diff)
downloadqemu-arm-bdea7dffd0afb0b4b18ad1b1ec8055771ccf93e1.tar.gz
linux-user: Fix getdents emulation for 64 bit guest on 32 bit hostdirent
Currently we mishandle emulation of the getdents syscall for the case of a 64 bit guest on a 32 bit host -- it defaults into the 'host and guest same size' codepath and generates incorrect structures in the guest buffer. We can't easily handle the 64-on-32 case using the host getdents syscall, because the guest struct dirent is bigger than the host struct dirent, and we might find the host syscall has handed us back more records than we can fit in the guest buffer after conversion. Instead, always emulate 64-on-32 getdents with the host getdents64. This avoids the buffer-overrun problem because a dirent64 struct is always the same size on any host and always larger than any architecture's dirent struct. Reported-by: Henry Wertz <hwertz10@gmail.com> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
-rw-r--r--linux-user/syscall.c18
1 files changed, 15 insertions, 3 deletions
diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 643b8833de..404be44ad5 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -259,10 +259,22 @@ static int gettid(void) {
return -ENOSYS;
}
#endif
-#if defined(TARGET_NR_getdents) && defined(__NR_getdents)
+
+/* For the 64-bit guest on 32-bit host case we must emulate
+ * getdents using getdents64, because otherwise the host
+ * might hand us back more dirent records than we can fit
+ * into the guest buffer after structure format conversion.
+ * Otherwise we emulate getdents with getdents if the host has it.
+ */
+#if defined(__NR_getdents) && HOST_LONG_BITS >= TARGET_ABI_BITS
+#define EMULATE_GETDENTS_WITH_GETDENTS
+#endif
+
+#if defined(TARGET_NR_getdents) && defined(EMULATE_GETDENTS_WITH_GETDENTS)
_syscall3(int, sys_getdents, uint, fd, struct linux_dirent *, dirp, uint, count);
#endif
-#if !defined(__NR_getdents) || \
+#if (defined(TARGET_NR_getdents) && \
+ !defined(EMULATE_GETDENTS_WITH_GETDENTS)) || \
(defined(TARGET_NR_getdents64) && defined(__NR_getdents64))
_syscall3(int, sys_getdents64, uint, fd, struct linux_dirent64 *, dirp, uint, count);
#endif
@@ -10163,7 +10175,7 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
#endif
#ifdef TARGET_NR_getdents
case TARGET_NR_getdents:
-#ifdef __NR_getdents
+#ifdef EMULATE_GETDENTS_WITH_GETDENTS
#if TARGET_ABI_BITS == 32 && HOST_LONG_BITS == 64
{
struct target_dirent *target_dirp;