linux-stable.git/fs/seq_file.c, branch v4.1.45

Make file credentials available to the seqfile interfaces

2017-09-10T20:35:50+00:00

[ Upstream commit 34dbbcdbf63360661ff7bda6c5f52f99ac515f92 ]

A lot of seqfile users seem to be using things like %pK that uses the
credentials of the current process, but that is actually completely
wrong for filesystem interfaces.

The unix semantics for permission checking files is to check permissions
at _open_ time, not at read or write time, and that is not just a small
detail: passing off stdin/stdout/stderr to a suid application and making
the actual IO happen in privileged context is a classic exploit
technique.

So if we want to be able to look at permissions at read time, we need to
use the file open credentials, not the current ones.  Normal file
accesses can just use "f_cred" (or any of the helper functions that do
that, like file_ns_capable()), but the seqfile interfaces do not have
any such options.

It turns out that seq_file _does_ save away the user_ns information of
the file, though.  Since user_ns is just part of the full credential
information, replace that special case with saving off the cred pointer
instead, and suddenly seq_file has all the permission information it
needs.

Signed-off-by: Linus Torvalds 
Signed-off-by: Sasha Levin

fs/seq_file: fix out-of-bounds read

2016-08-31T23:21:09+00:00

[ Upstream commit 088bf2ff5d12e2e32ee52a4024fec26e582f44d3 ]

seq_read() is a nasty piece of work, not to mention buggy.

It has (I think) an old bug which allows unprivileged userspace to read
beyond the end of m->buf.

I was getting these:

    BUG: KASAN: slab-out-of-bounds in seq_read+0xcd2/0x1480 at addr ffff880116889880
    Read of size 2713 by task trinity-c2/1329
    CPU: 2 PID: 1329 Comm: trinity-c2 Not tainted 4.8.0-rc1+ #96
    Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.9.3-0-ge2fc41e-prebuilt.qemu-project.org 04/01/2014
    Call Trace:
      kasan_object_err+0x1c/0x80
      kasan_report_error+0x2cb/0x7e0
      kasan_report+0x4e/0x80
      check_memory_region+0x13e/0x1a0
      kasan_check_read+0x11/0x20
      seq_read+0xcd2/0x1480
      proc_reg_read+0x10b/0x260
      do_loop_readv_writev.part.5+0x140/0x2c0
      do_readv_writev+0x589/0x860
      vfs_readv+0x7b/0xd0
      do_readv+0xd8/0x2c0
      SyS_readv+0xb/0x10
      do_syscall_64+0x1b3/0x4b0
      entry_SYSCALL64_slow_path+0x25/0x25
    Object at ffff880116889100, in cache kmalloc-4096 size: 4096
    Allocated:
    PID = 1329
      save_stack_trace+0x26/0x80
      save_stack+0x46/0xd0
      kasan_kmalloc+0xad/0xe0
      __kmalloc+0x1aa/0x4a0
      seq_buf_alloc+0x35/0x40
      seq_read+0x7d8/0x1480
      proc_reg_read+0x10b/0x260
      do_loop_readv_writev.part.5+0x140/0x2c0
      do_readv_writev+0x589/0x860
      vfs_readv+0x7b/0xd0
      do_readv+0xd8/0x2c0
      SyS_readv+0xb/0x10
      do_syscall_64+0x1b3/0x4b0
      return_from_SYSCALL_64+0x0/0x6a
    Freed:
    PID = 0
    (stack is not available)
    Memory state around the buggy address:
     ffff88011688a000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
     ffff88011688a080: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    >ffff88011688a100: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
		       ^
     ffff88011688a180: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
     ffff88011688a200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
    ==================================================================
    Disabling lock debugging due to kernel taint

This seems to be the same thing that Dave Jones was seeing here:

  https://lkml.org/lkml/2016/8/12/334

There are multiple issues here:

  1) If we enter the function with a non-empty buffer, there is an attempt
     to flush it. But it was not clearing m->from after doing so, which
     means that if we try to do this flush twice in a row without any call
     to traverse() in between, we are going to be reading from the wrong
     place -- the splat above, fixed by this patch.

  2) If there's a short write to userspace because of page faults, the
     buffer may already contain multiple lines (i.e. pos has advanced by
     more than 1), but we don't save the progress that was made so the
     next call will output what we've already returned previously. Since
     that is a much less serious issue (and I have a headache after
     staring at seq_read() for the past 8 hours), I'll leave that for now.

Link: http://lkml.kernel.org/r/1471447270-32093-1-git-send-email-vegard.nossum@oracle.com
Signed-off-by: Vegard Nossum 
Reported-by: Dave Jones 
Cc: Al Viro 
Cc: 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds 
Signed-off-by: Sasha Levin

bitmap, cpumask, nodemask: remove dedicated formatting functions

2015-02-14T05:21:39+00:00

Now that all bitmap formatting usages have been converted to
'%*pb[l]', the separate formatting functions are unnecessary.  The
following functions are removed.

* bitmap_scn[list]printf()
* cpumask_scnprintf(), cpulist_scnprintf()
* [__]nodemask_scnprintf(), [__]nodelist_scnprintf()
* seq_bitmap[_list](), seq_cpumask[_list](), seq_nodemask[_list]()
* seq_buf_bitmask()

Signed-off-by: Tejun Heo 
Cc: Rusty Russell 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

fs, seq_file: fallback to vmalloc instead of oom kill processes

2014-12-13T20:42:49+00:00

Since commit 058504edd026 ("fs/seq_file: fallback to vmalloc allocation"),
seq_buf_alloc() falls back to vmalloc() when the kmalloc() for contiguous
memory fails.  This was done to address order-4 slab allocations for
reading /proc/stat on large machines and noticed because
PAGE_ALLOC_COSTLY_ORDER < 4, so there is no infinite loop in the page
allocator when allocating new slab for such high-order allocations.

Contiguous memory isn't necessary for caller of seq_buf_alloc(), however.
Other GFP_KERNEL high-order allocations that are <=
PAGE_ALLOC_COSTLY_ORDER will simply loop forever in the page allocator and
oom kill processes as a result.

We don't want to kill processes so that we can allocate contiguous memory
in situations when contiguous memory isn't necessary.

This patch does the kmalloc() allocation with __GFP_NORETRY for high-order
allocations.  This still utilizes memory compaction and direct reclaim in
the allocation path, the only difference is that it will fail immediately
instead of oom kill processes when out of memory.

[akpm@linux-foundation.org: add comment]
Signed-off-by: David Rientjes 
Cc: Heiko Carstens 
Cc: Christoph Hellwig 
Cc: Al Viro 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

seq_file: Rename seq_overflow() to seq_has_overflowed() and make public

2014-10-30T00:26:06+00:00

The return values of seq_printf/puts/putc are frequently misused.

Start down a path to remove all the return value uses of these
functions.

Move the seq_overflow() to a global inlined function called
seq_has_overflowed() that can be used by the users of seq_file() calls.

Update the documentation to not show return types for seq_printf
et al.  Add a description of seq_has_overflowed().

Link: http://lkml.kernel.org/p/848ac7e3d1c31cddf638a8526fa3c59fa6fdeb8a.1412031505.git.joe@perches.com

Cc: Al Viro 
Signed-off-by: Joe Perches 
[ Reworked the original patch from Joe ]
Signed-off-by: Steven Rostedt

fs/seq_file: fallback to vmalloc allocation

2014-07-03T16:21:54+00:00

There are a couple of seq_files which use the single_open() interface.
This interface requires that the whole output must fit into a single
buffer.

E.g.  for /proc/stat allocation failures have been observed because an
order-4 memory allocation failed due to memory fragmentation.  In such
situations reading /proc/stat is not possible anymore.

Therefore change the seq_file code to fallback to vmalloc allocations
which will usually result in a couple of order-0 allocations and hence
also work if memory is fragmented.

For reference a call trace where reading from /proc/stat failed:

  sadc: page allocation failure: order:4, mode:0x1040d0
  CPU: 1 PID: 192063 Comm: sadc Not tainted 3.10.0-123.el7.s390x #1
  [...]
  Call Trace:
    show_stack+0x6c/0xe8
    warn_alloc_failed+0xd6/0x138
    __alloc_pages_nodemask+0x9da/0xb68
    __get_free_pages+0x2e/0x58
    kmalloc_order_trace+0x44/0xc0
    stat_open+0x5a/0xd8
    proc_reg_open+0x8a/0x140
    do_dentry_open+0x1bc/0x2c8
    finish_open+0x46/0x60
    do_last+0x382/0x10d0
    path_openat+0xc8/0x4f8
    do_filp_open+0x46/0xa8
    do_sys_open+0x114/0x1f0
    sysc_tracego+0x14/0x1a

Signed-off-by: Heiko Carstens 
Tested-by: David Rientjes 
Cc: Ian Kent 
Cc: Hendrik Brueckner 
Cc: Thorsten Diehl 
Cc: Andrea Righi 
Cc: Christoph Hellwig 
Cc: Al Viro 
Cc: Stefan Bader 
Cc: 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

seq_file: always clear m->count when we free m->buf

2013-11-19T03:07:53+00:00

Once we'd freed m->buf, m->count should become zero - we have no valid
contents reachable via m->buf.

Reported-by: Charley (Hao Chuan) Chu 
Signed-off-by: Al Viro 
Signed-off-by: Linus Torvalds

seq_file: introduce seq_setwidth() and seq_pad()

2013-11-15T00:32:20+00:00

There are several users who want to know bytes written by seq_*() for
alignment purpose.  Currently they are using %n format for knowing it
because seq_*() returns 0 on success.

This patch introduces seq_setwidth() and seq_pad() for allowing them to
align without using %n format.

Signed-off-by: Tetsuo Handa 
Signed-off-by: Kees Cook 
Cc: Joe Perches 
Cc: David Miller 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

seq_file: always update file->f_pos in seq_lseek()

2013-10-25T14:46:40+00:00

This issue was first pointed out by Jiaxing Wang several months ago, but no
further comments:
https://lkml.org/lkml/2013/6/29/41

As we know pread() does not change f_pos, so after pread(), file->f_pos
and m->read_pos become different. And seq_lseek() does not update file->f_pos
if offset equals to m->read_pos, so after pread() and seq_lseek()(lseek to
m->read_pos), then a subsequent read may read from a wrong position, the
following program produces the problem:

    char str1[32] = { 0 };
    char str2[32] = { 0 };
    int poffset = 10;
    int count = 20;

    /*open any seq file*/
    int fd = open("/proc/modules", O_RDONLY);

    pread(fd, str1, count, poffset);
    printf("pread:%s\n", str1);

    /*seek to where m->read_pos is*/
    lseek(fd, poffset+count, SEEK_SET);

    /*supposed to read from poffset+count, but this read from position 0*/
    read(fd, str2, count);
    printf("read:%s\n", str2);

out put:
pread:
 ck_netbios_ns 12665
read:
 nf_conntrack_netbios

/proc/modules:
nf_conntrack_netbios_ns 12665 0 - Live 0xffffffffa038b000
nf_conntrack_broadcast 12589 1 nf_conntrack_netbios_ns, Live 0xffffffffa0386000

So we always update file->f_pos to offset in seq_lseek() to fix this issue.

Signed-off-by: Jiaxing Wang 
Signed-off-by: Gu Zheng 
Signed-off-by: Al Viro

seq_file: add seq_list_*_percpu helpers

2013-07-08T09:36:41+00:00

When we convert the file_lock_list to a set of percpu lists, we'll need
a way to iterate over them in order to output /proc/locks info. Add
some seq_list_*_percpu helpers to handle that.

Signed-off-by: Jeff Layton 
Acked-by: J. Bruce Fields 
Signed-off-by: Al Viro