[RFC PATCH v2] compat: poll() in 32-bit applications does not handle negative timeout values properly on 64-bit kernels

[Josh Hunt <johunt@akamai.com>]

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We have hit an issue where our 32-bit applications using poll() and
passing in a value of -1 for the timeout value return after ~49 days
(2^32 msec), instead of waiting indefinitely. I've instrumented the
kernel and found we are hitting the case where poll() believes we've
passed in a positive number and thus creates a timespec, etc. I've
implemented compat_sys_poll() to sign-extend the timeout value and
resolve the issue.

There was an almost identical patch submitted last year, but for
whatever reason did not make it in:
https://lkml.org/lkml/2011/9/18/19

I am guessing there are other architectures affected by this bug. This
patch only fixes x86.

Josh

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commit cde9eb901ccb3b5af3e501b018b90f16c53942c2
Author: Josh Hunt <johunt@akamai.com>
Date:   Mon Feb 6 20:51:31 2012 -0800

    compat: poll() in 32-bit applications does not handle negative timeout values properly on 64-bit kernels

    We have observed our 32-bit applications running on 64-bit kernels do not
    wait infinitely when passed a negative value for the timeout argument.
    Instead we see poll() returning in ~49 days or 2^32 msecs, because the
    timeout argument is not getting sign-extended. Implementing
    compat_sys_poll() to handle this case.

    Reported-by: Phil Lisiecki <lisiecki@akamai.com>
    Signed-off-by: Josh Hunt <johunt@akamai.com>
    Cc: <stable@vger.kernel.org>

diff --git a/arch/x86/syscalls/syscall_32.tbl b/arch/x86/syscalls/syscall_32.tbl
index ce98e28..8407150 100644
--- a/arch/x86/syscalls/syscall_32.tbl
+++ b/arch/x86/syscalls/syscall_32.tbl
@@ -174,7 +174,7 @@
 165	i386	getresuid		sys_getresuid16
 166	i386	vm86			ptregs_vm86			sys32_vm86_warning
 167	i386	query_module
-168	i386	poll			sys_poll
+168	i386	poll			sys_poll			compat_sys_poll
 169	i386	nfsservctl
 170	i386	setresgid		sys_setresgid16
 171	i386	getresgid		sys_getresgid16
diff --git a/fs/compat.c b/fs/compat.c
index fa9d721..77bd50e 100644
--- a/fs/compat.c
+++ b/fs/compat.c
@@ -1611,6 +1611,12 @@ asmlinkage long compat_sys_pselect6(int n, compat_ulong_t __user *inp,
 				 sigsetsize);
 }
 
+asmlinkage long compat_sys_poll(struct pollfd __user *ufds, unsigned int nfds,
+	int timeout_msecs)
+{
+	return sys_poll(ufds, nfds, timeout_msecs);
+}
+
 asmlinkage long compat_sys_ppoll(struct pollfd __user *ufds,
 	unsigned int nfds, struct compat_timespec __user *tsp,
 	const compat_sigset_t __user *sigmask, compat_size_t sigsetsize)
diff --git a/include/linux/compat.h b/include/linux/compat.h
index 41c9f65..66e61e0 100644
--- a/include/linux/compat.h
+++ b/include/linux/compat.h
@@ -433,6 +433,8 @@ asmlinkage long compat_sys_pselect6(int n, compat_ulong_t __user *inp,
 				    compat_ulong_t __user *exp,
 				    struct compat_timespec __user *tsp,
 				    void __user *sig);
+asmlinkage long compat_sys_poll(struct pollfd __user *ufds, unsigned int nfds,
+				int timeout_msecs);
 asmlinkage long compat_sys_ppoll(struct pollfd __user *ufds,
 				 unsigned int nfds,
 				 struct compat_timespec __user *tsp,