linux-stable.git/fs/proc/base.c, branch v5.14.2

procfs: allow reading fdinfo with PTRACE_MODE_READ

2021-07-01T18:06:04+00:00

Android captures per-process system memory state when certain low memory
events (e.g a foreground app kill) occur, to identify potential memory
hoggers.  In order to measure how much memory a process actually consumes,
it is necessary to include the DMA buffer sizes for that process in the
memory accounting.  Since the handle to DMA buffers are raw FDs, it is
important to be able to identify which processes have FD references to a
DMA buffer.

Currently, DMA buffer FDs can be accounted using /proc//fd/* and
/proc//fdinfo -- both are only readable by the process owner, as
follows:

  1. Do a readlink on each FD.
  2. If the target path begins with "/dmabuf", then the FD is a dmabuf FD.
  3. stat the file to get the dmabuf inode number.
  4. Read/ proc//fdinfo/, to get the DMA buffer size.

Accessing other processes' fdinfo requires root privileges.  This limits
the use of the interface to debugging environments and is not suitable for
production builds.  Granting root privileges even to a system process
increases the attack surface and is highly undesirable.

Since fdinfo doesn't permit reading process memory and manipulating
process state, allow accessing fdinfo under PTRACE_MODE_READ_FSCRED.

Link: https://lkml.kernel.org/r/20210308170651.919148-1-kaleshsingh@google.com
Signed-off-by: Kalesh Singh 
Suggested-by: Jann Horn 
Acked-by: Christian König 
Cc: Alexander Viro 
Cc: Alexey Dobriyan 
Cc: Alexey Gladkov 
Cc: Andrei Vagin 
Cc: Bernd Edlinger 
Cc: Christian Brauner 
Cc: Eric W. Biederman 
Cc: Helge Deller 
Cc: Hridya Valsaraju 
Cc: James Morris 
Cc: Jeff Vander Stoep 
Cc: Jonathan Corbet 
Cc: Kees Cook 
Cc: Matthew Wilcox 
Cc: Mauro Carvalho Chehab 
Cc: Michal Hocko 
Cc: Michel Lespinasse 
Cc: Minchan Kim 
Cc: Randy Dunlap 
Cc: Suren Baghdasaryan 
Cc: Szabolcs Nagy 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

proc: Avoid mixing integer types in mem_rw()

2021-07-01T18:06:04+00:00

Use size_t when capping the count argument received by mem_rw(). Since
count is size_t, using min_t(int, ...) can lead to a negative value
that will later be passed to access_remote_vm(), which can cause
unexpected behavior.

Since we are capping the value to at maximum PAGE_SIZE, the conversion
from size_t to int when passing it to access_remote_vm() as "len"
shouldn't be a problem.

Link: https://lkml.kernel.org/r/20210512125215.3348316-1-marcelo.cerri@canonical.com
Reviewed-by: David Disseldorp 
Signed-off-by: Thadeu Lima de Souza Cascardo 
Signed-off-by: Marcelo Henrique Cerri 
Cc: Alexey Dobriyan 
Cc: Souza Cascardo 
Cc: Christian Brauner 
Cc: Michel Lespinasse 
Cc: Helge Deller 
Cc: Oleg Nesterov 
Cc: Lorenzo Stoakes 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

proc: only require mm_struct for writing

2021-06-15T17:47:51+00:00

Commit 591a22c14d3f ("proc: Track /proc/$pid/attr/ opener mm_struct") we
started using __mem_open() to track the mm_struct at open-time, so that
we could then check it for writes.

But that also ended up making the permission checks at open time much
stricter - and not just for writes, but for reads too.  And that in turn
caused a regression for at least Fedora 29, where NIC interfaces fail to
start when using NetworkManager.

Since only the write side wanted the mm_struct test, ignore any failures
by __mem_open() at open time, leaving reads unaffected.  The write()
time verification of the mm_struct pointer will then catch the failure
case because a NULL pointer will not match a valid 'current->mm'.

Link: https://lore.kernel.org/netdev/YMjTlp2FSJYvoyFa@unreal/
Fixes: 591a22c14d3f ("proc: Track /proc/$pid/attr/ opener mm_struct")
Reported-and-tested-by: Leon Romanovsky 
Cc: Kees Cook 
Cc: Christian Brauner 
Cc: Andrea Righi 
Signed-off-by: Linus Torvalds

proc: Track /proc/$pid/attr/ opener mm_struct

2021-06-08T17:24:09+00:00

Commit bfb819ea20ce ("proc: Check /proc/$pid/attr/ writes against file opener")
tried to make sure that there could not be a confusion between the opener of
a /proc/$pid/attr/ file and the writer. It used struct cred to make sure
the privileges didn't change. However, there were existing cases where a more
privileged thread was passing the opened fd to a differently privileged thread
(during container setup). Instead, use mm_struct to track whether the opener
and writer are still the same process. (This is what several other proc files
already do, though for different reasons.)

Reported-by: Christian Brauner 
Reported-by: Andrea Righi 
Tested-by: Andrea Righi 
Fixes: bfb819ea20ce ("proc: Check /proc/$pid/attr/ writes against file opener")
Cc: stable@vger.kernel.org
Signed-off-by: Kees Cook 
Signed-off-by: Linus Torvalds

proc: Check /proc/$pid/attr/ writes against file opener

2021-05-25T20:24:41+00:00

Fix another "confused deputy" weakness[1]. Writes to /proc/$pid/attr/
files need to check the opener credentials, since these fds do not
transition state across execve(). Without this, it is possible to
trick another process (which may have different credentials) to write
to its own /proc/$pid/attr/ files, leading to unexpected and possibly
exploitable behaviors.

[1] https://www.kernel.org/doc/html/latest/security/credentials.html?highlight=confused#open-file-credentials

Fixes: 1da177e4c3f41 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Signed-off-by: Kees Cook 
Signed-off-by: Linus Torvalds

proc/wchan: use printk format instead of lookup_symbol_name()

2021-02-26T17:41:03+00:00

To resolve the symbol fuction name for wchan, use the printk format
specifier %ps instead of manually looking up the symbol function name
via lookup_symbol_name().

Link: https://lkml.kernel.org/r/20201217165413.GA1959@ls3530.fritz.box
Signed-off-by: Helge Deller 
Cc: Alexey Dobriyan 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

fs: make helpers idmap mount aware

2021-01-24T13:27:20+00:00

Extend some inode methods with an additional user namespace argument. A
filesystem that is aware of idmapped mounts will receive the user
namespace the mount has been marked with. This can be used for
additional permission checking and also to enable filesystems to
translate between uids and gids if they need to. We have implemented all
relevant helpers in earlier patches.

As requested we simply extend the exisiting inode method instead of
introducing new ones. This is a little more code churn but it's mostly
mechanical and doesnt't leave us with additional inode methods.

Link: https://lore.kernel.org/r/20210121131959.646623-25-christian.brauner@ubuntu.com
Cc: Christoph Hellwig 
Cc: David Howells 
Cc: Al Viro 
Cc: linux-fsdevel@vger.kernel.org
Reviewed-by: Christoph Hellwig 
Signed-off-by: Christian Brauner

stat: handle idmapped mounts

2021-01-24T13:27:17+00:00

The generic_fillattr() helper fills in the basic attributes associated
with an inode. Enable it to handle idmapped mounts. If the inode is
accessed through an idmapped mount map it into the mount's user
namespace before we store the uid and gid. If the initial user namespace
is passed nothing changes so non-idmapped mounts will see identical
behavior as before.

Link: https://lore.kernel.org/r/20210121131959.646623-12-christian.brauner@ubuntu.com
Cc: Christoph Hellwig 
Cc: David Howells 
Cc: Al Viro 
Cc: linux-fsdevel@vger.kernel.org
Reviewed-by: Christoph Hellwig 
Reviewed-by: James Morris 
Signed-off-by: Christian Brauner

attr: handle idmapped mounts

2021-01-24T13:27:16+00:00

When file attributes are changed most filesystems rely on the
setattr_prepare(), setattr_copy(), and notify_change() helpers for
initialization and permission checking. Let them handle idmapped mounts.
If the inode is accessed through an idmapped mount map it into the
mount's user namespace. Afterwards the checks are identical to
non-idmapped mounts. If the initial user namespace is passed nothing
changes so non-idmapped mounts will see identical behavior as before.

Helpers that perform checks on the ia_uid and ia_gid fields in struct
iattr assume that ia_uid and ia_gid are intended values and have already
been mapped correctly at the userspace-kernelspace boundary as we
already do today. If the initial user namespace is passed nothing
changes so non-idmapped mounts will see identical behavior as before.

Link: https://lore.kernel.org/r/20210121131959.646623-8-christian.brauner@ubuntu.com
Cc: Christoph Hellwig 
Cc: David Howells 
Cc: Al Viro 
Cc: linux-fsdevel@vger.kernel.org
Reviewed-by: Christoph Hellwig 
Signed-off-by: Christian Brauner

namei: make permission helpers idmapped mount aware

2021-01-24T13:27:16+00:00

The two helpers inode_permission() and generic_permission() are used by
the vfs to perform basic permission checking by verifying that the
caller is privileged over an inode. In order to handle idmapped mounts
we extend the two helpers with an additional user namespace argument.
On idmapped mounts the two helpers will make sure to map the inode
according to the mount's user namespace and then peform identical
permission checks to inode_permission() and generic_permission(). If the
initial user namespace is passed nothing changes so non-idmapped mounts
will see identical behavior as before.

Link: https://lore.kernel.org/r/20210121131959.646623-6-christian.brauner@ubuntu.com
Cc: Christoph Hellwig 
Cc: David Howells 
Cc: Al Viro 
Cc: linux-fsdevel@vger.kernel.org
Reviewed-by: Christoph Hellwig 
Reviewed-by: James Morris 
Acked-by: Serge Hallyn 
Signed-off-by: Christian Brauner