From 20279c305ece6a458006999c8dafc5672ca92803 Mon Sep 17 00:00:00 2001 From: Ian Lewis Date: Tue, 26 Nov 2019 18:19:47 -0800 Subject: Allow open(O_TRUNC) and (f)truncate for proc files. This allows writable proc and devices files to be opened with O_CREAT|O_TRUNC. This is encountered most frequently when interacting with proc or devices files via the command line. e.g. $ echo 8192 1048576 4194304 > /proc/sys/net/ipv4/tcp_rmem Also adds a test to test the behavior of open(O_TRUNC), truncate, and ftruncate on named pipes. Fixes #1116 PiperOrigin-RevId: 282677425 --- pkg/sentry/syscalls/linux/sys_file.go | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) (limited to 'pkg/sentry/syscalls/linux') diff --git a/pkg/sentry/syscalls/linux/sys_file.go b/pkg/sentry/syscalls/linux/sys_file.go index 167c2b60b..3b9181002 100644 --- a/pkg/sentry/syscalls/linux/sys_file.go +++ b/pkg/sentry/syscalls/linux/sys_file.go @@ -171,6 +171,9 @@ func openAt(t *kernel.Task, dirFD int32, addr usermem.Addr, flags uint) (fd uint } } + // Truncate is called when O_TRUNC is specified for any kind of + // existing Dirent. Behavior is delegated to the entry's Truncate + // implementation. if flags&linux.O_TRUNC != 0 { if err := d.Inode.Truncate(t, d, 0); err != nil { return err @@ -397,7 +400,9 @@ func createAt(t *kernel.Task, dirFD int32, addr usermem.Addr, flags uint, mode l return err } - // Should we truncate the file? + // Truncate is called when O_TRUNC is specified for any kind of + // existing Dirent. Behavior is delegated to the entry's Truncate + // implementation. if flags&linux.O_TRUNC != 0 { if err := found.Inode.Truncate(t, found, 0); err != nil { return err @@ -1484,6 +1489,8 @@ func Truncate(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.Sysc if fs.IsDir(d.Inode.StableAttr) { return syserror.EISDIR } + // In contrast to open(O_TRUNC), truncate(2) is only valid for file + // types. if !fs.IsFile(d.Inode.StableAttr) { return syserror.EINVAL } @@ -1522,7 +1529,8 @@ func Ftruncate(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.Sys return 0, nil, syserror.EINVAL } - // Note that this is different from truncate(2) above, where a + // In contrast to open(O_TRUNC), truncate(2) is only valid for file + // types. Note that this is different from truncate(2) above, where a // directory returns EISDIR. if !fs.IsFile(file.Dirent.Inode.StableAttr) { return 0, nil, syserror.EINVAL -- cgit v1.2.3