From 2b3f64cbf3e00f5042d120b4c23ed66078431f8c Mon Sep 17 00:00:00 2001 From: Peter Maydell Date: Thu, 19 Apr 2018 13:57:40 +0100 Subject: [PATCH] linux-user: Fix getdents emulation for 64 bit guest on 32 bit host 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 Signed-off-by: Peter Maydell Message-Id: <20180419125740.2695-1-peter.maydell@linaro.org> Signed-off-by: Laurent Vivier --- linux-user/syscall.c | 18 +++++++++++++++--- 1 file 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;