From 0a489cb3b6a7b277030cdbc97c2c65905db94536 Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Tue, 18 Apr 2006 13:02:48 -0700 Subject: [PATCH] x86: don't allow tail-calls in sys_ftruncate[64]() Gcc thinks it owns the incoming argument stack, but that's not true for "asmlinkage" functions, and it corrupts the caller-set-up argument stack when it pushes the third argument onto the stack. Which can result in %ebx getting corrupted in user space. Now, normally nobody sane would ever notice, since libc will save and restore %ebx anyway over the system call, but it's still wrong. I'd much rather have "asmlinkage" tell gcc directly that it doesn't own the stack, but no such attribute exists, so we're stuck with our hacky manual "prevent_tail_call()" macro once more (we've had the same issue before with sys_waitpid() and sys_wait4()). Thanks to Hans-Werner Hilse for reporting the issue and testing the fix. Signed-off-by: Linus Torvalds --- fs/open.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/fs/open.c b/fs/open.c index c32c89d6d8d..8279c65d3be 100644 --- a/fs/open.c +++ b/fs/open.c @@ -331,7 +331,9 @@ out: asmlinkage long sys_ftruncate(unsigned int fd, unsigned long length) { - return do_sys_ftruncate(fd, length, 1); + long ret = do_sys_ftruncate(fd, length, 1); + prevent_tail_call(ret); + return ret; } /* LFS versions of truncate are only needed on 32 bit machines */ @@ -343,7 +345,9 @@ asmlinkage long sys_truncate64(const char __user * path, loff_t length) asmlinkage long sys_ftruncate64(unsigned int fd, loff_t length) { - return do_sys_ftruncate(fd, length, 0); + long ret = do_sys_ftruncate(fd, length, 0); + prevent_tail_call(ret); + return ret; } #endif -- 2.20.1