From 82e43e2a64739caf323ac98641e1250c3808c300 Mon Sep 17 00:00:00 2001 From: Ian Kent Date: Wed, 22 Feb 2012 20:45:44 +0800 Subject: autofs: work around unhappy compat problem on x86-64 commit a32744d4abae24572eff7269bc17895c41bd0085 upstream. When the autofs protocol version 5 packet type was added in commit 5c0a32fc2cd0 ("autofs4: add new packet type for v5 communications"), it obvously tried quite hard to be word-size agnostic, and uses explicitly sized fields that are all correctly aligned. However, with the final "char name[NAME_MAX+1]" array at the end, the actual size of the structure ends up being not very well defined: because the struct isn't marked 'packed', doing a "sizeof()" on it will align the size of the struct up to the biggest alignment of the members it has. And despite all the members being the same, the alignment of them is different: a "__u64" has 4-byte alignment on x86-32, but native 8-byte alignment on x86-64. And while 'NAME_MAX+1' ends up being a nice round number (256), the name[] array starts out a 4-byte aligned. End result: the "packed" size of the structure is 300 bytes: 4-byte, but not 8-byte aligned. As a result, despite all the fields being in the same place on all architectures, sizeof() will round up that size to 304 bytes on architectures that have 8-byte alignment for u64. Note that this is *not* a problem for 32-bit compat mode on POWER, since there __u64 is 8-byte aligned even in 32-bit mode. But on x86, 32-bit and 64-bit alignment is different for 64-bit entities, and as a result the structure that has exactly the same layout has different sizes. So on x86-64, but no other architecture, we will just subtract 4 from the size of the structure when running in a compat task. That way we will write the properly sized packet that user mode expects. Not pretty. Sadly, this very subtle, and unnecessary, size difference has been encoded in user space that wants to read packets of *exactly* the right size, and will refuse to touch anything else. Reported-and-tested-by: Thomas Meyer Signed-off-by: Ian Kent Signed-off-by: Linus Torvalds Cc: Jonathan Nieder Signed-off-by: Greg Kroah-Hartman --- fs/autofs4/autofs_i.h | 1 + fs/autofs4/dev-ioctl.c | 1 + fs/autofs4/inode.c | 2 ++ fs/autofs4/waitq.c | 22 +++++++++++++++++++--- 4 files changed, 23 insertions(+), 3 deletions(-) (limited to 'fs') diff --git a/fs/autofs4/autofs_i.h b/fs/autofs4/autofs_i.h index 8f7cdde41733..5d8d9a0110bb 100644 --- a/fs/autofs4/autofs_i.h +++ b/fs/autofs4/autofs_i.h @@ -125,6 +125,7 @@ struct autofs_sb_info { int sub_version; int min_proto; int max_proto; + int compat_daemon; unsigned long exp_timeout; unsigned int type; int reghost_enabled; diff --git a/fs/autofs4/dev-ioctl.c b/fs/autofs4/dev-ioctl.c index 00bf8fcb245f..5bb5a2afb144 100644 --- a/fs/autofs4/dev-ioctl.c +++ b/fs/autofs4/dev-ioctl.c @@ -389,6 +389,7 @@ static int autofs_dev_ioctl_setpipefd(struct file *fp, sbi->pipefd = pipefd; sbi->pipe = pipe; sbi->catatonic = 0; + sbi->compat_daemon = is_compat_task(); } out: mutex_unlock(&sbi->wq_mutex); diff --git a/fs/autofs4/inode.c b/fs/autofs4/inode.c index 69c8142da838..0ca145af8509 100644 --- a/fs/autofs4/inode.c +++ b/fs/autofs4/inode.c @@ -19,6 +19,7 @@ #include #include #include +#include #include "autofs_i.h" #include @@ -341,6 +342,7 @@ int autofs4_fill_super(struct super_block *s, void *data, int silent) set_autofs_type_indirect(&sbi->type); sbi->min_proto = 0; sbi->max_proto = 0; + sbi->compat_daemon = is_compat_task(); mutex_init(&sbi->wq_mutex); spin_lock_init(&sbi->fs_lock); sbi->queues = NULL; diff --git a/fs/autofs4/waitq.c b/fs/autofs4/waitq.c index 2341375386f8..136a0d6914c6 100644 --- a/fs/autofs4/waitq.c +++ b/fs/autofs4/waitq.c @@ -90,7 +90,24 @@ static int autofs4_write(struct file *file, const void *addr, int bytes) return (bytes > 0); } - + +/* + * The autofs_v5 packet was misdesigned. + * + * The packets are identical on x86-32 and x86-64, but have different + * alignment. Which means that 'sizeof()' will give different results. + * Fix it up for the case of running 32-bit user mode on a 64-bit kernel. + */ +static noinline size_t autofs_v5_packet_size(struct autofs_sb_info *sbi) +{ + size_t pktsz = sizeof(struct autofs_v5_packet); +#if defined(CONFIG_X86_64) && defined(CONFIG_COMPAT) + if (sbi->compat_daemon > 0) + pktsz -= 4; +#endif + return pktsz; +} + static void autofs4_notify_daemon(struct autofs_sb_info *sbi, struct autofs_wait_queue *wq, int type) @@ -147,8 +164,7 @@ static void autofs4_notify_daemon(struct autofs_sb_info *sbi, { struct autofs_v5_packet *packet = &pkt.v5_pkt.v5_packet; - pktsz = sizeof(*packet); - + pktsz = autofs_v5_packet_size(sbi); packet->wait_queue_token = wq->wait_queue_token; packet->len = wq->name.len; memcpy(packet->name, wq->name.name, wq->name.len); -- cgit v1.2.3