From 04c95f4da7f657a0bef17d115d0a5ca2ac0e2d22 Mon Sep 17 00:00:00 2001 From: Peter Maydell Date: Mon, 18 Jul 2016 15:36:00 +0100 Subject: linux-user: Don't use alloca() for epoll_wait's epoll event array The epoll event array which epoll_wait() allocates has a size determined by the guest which could potentially be quite large. Use g_try_new() rather than alloca() so that we can fail more cleanly if the guest hands us an oversize value. (ENOMEM is not a documented return value for epoll_wait() but in practice some kernel configurations can return it -- see for instance sys_oabi_epoll_wait() on ARM.) This rearrangement includes fixing a bug where we were incorrectly passing a negative length to unlock_user() in the error-exit codepath. Signed-off-by: Peter Maydell Signed-off-by: Riku Voipio --- linux-user/syscall.c | 17 +++++++++++++---- 1 file changed, 13 insertions(+), 4 deletions(-) diff --git a/linux-user/syscall.c b/linux-user/syscall.c index 31143b38fe..932d0ecec3 100644 --- a/linux-user/syscall.c +++ b/linux-user/syscall.c @@ -11777,7 +11777,12 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1, goto efault; } - ep = alloca(maxevents * sizeof(struct epoll_event)); + ep = g_try_new(struct epoll_event, maxevents); + if (!ep) { + unlock_user(target_ep, arg2, 0); + ret = -TARGET_ENOMEM; + break; + } switch (num) { #if defined(TARGET_NR_epoll_pwait) @@ -11795,8 +11800,8 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1, target_set = lock_user(VERIFY_READ, arg5, sizeof(target_sigset_t), 1); if (!target_set) { - unlock_user(target_ep, arg2, 0); - goto efault; + ret = -TARGET_EFAULT; + break; } target_to_host_sigset(set, target_set); unlock_user(target_set, arg5, 0); @@ -11824,8 +11829,12 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1, target_ep[i].events = tswap32(ep[i].events); target_ep[i].data.u64 = tswap64(ep[i].data.u64); } + unlock_user(target_ep, arg2, + ret * sizeof(struct target_epoll_event)); + } else { + unlock_user(target_ep, arg2, 0); } - unlock_user(target_ep, arg2, ret * sizeof(struct target_epoll_event)); + g_free(ep); break; } #endif -- cgit v1.2.3