diff options
author | Daniel Axtens <dja@axtens.net> | 2021-09-20 01:12:24 +1000 |
---|---|---|
committer | Daniel Kiper <daniel.kiper@oracle.com> | 2022-06-07 16:39:33 +0200 |
commit | ee9652031491326736714a988fbbaeab8ef9255c (patch) | |
tree | 22ed1838457b27cd7a3f138c7e38d78398bc98b2 | |
parent | 96abf4fb9d829f4a405d5df39bc74bbccbd0e322 (diff) | |
download | grub-ee9652031491326736714a988fbbaeab8ef9255c.tar.gz |
net/tftp: Prevent a UAF and double-free from a failed seek
A malicious tftp server can cause UAFs and a double free.
An attempt to read from a network file is handled by grub_net_fs_read(). If
the read is at an offset other than the current offset, grub_net_seek_real()
is invoked.
In grub_net_seek_real(), if a backwards seek cannot be satisfied from the
currently received packets, and the underlying transport does not provide
a seek method, then grub_net_seek_real() will close and reopen the network
protocol layer.
For tftp, the ->close() call goes to tftp_close() and frees the tftp_data_t
file->data. The file->data pointer is not nulled out after the free.
If the ->open() call fails, the file->data will not be reallocated and will
continue point to a freed memory block. This could happen from a server
refusing to send the requisite ack to the new tftp request, for example.
The seek and the read will then fail, but the grub_file continues to exist:
the failed seek does not necessarily cause the entire file to be thrown
away (e.g. where the file is checked to see if it is gzipped/lzio/xz/etc.,
a read failure is interpreted as a decompressor passing on the file, not as
an invalidation of the entire grub_file_t structure).
This means subsequent attempts to read or seek the file will use the old
file->data after free. Eventually, the file will be close()d again and
file->data will be freed again.
Mark a net_fs file that doesn't reopen as broken. Do not permit read() or
close() on a broken file (seek is not exposed directly to the file API -
it is only called as part of read, so this blocks seeks as well).
As an additional defence, null out the ->data pointer if tftp_open() fails.
That would have lead to a simple null pointer dereference rather than
a mess of UAFs.
This may affect other protocols, I haven't checked.
Signed-off-by: Daniel Axtens <dja@axtens.net>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
-rw-r--r-- | grub-core/net/net.c | 11 | ||||
-rw-r--r-- | grub-core/net/tftp.c | 1 | ||||
-rw-r--r-- | include/grub/net.h | 1 |
3 files changed, 11 insertions, 2 deletions
diff --git a/grub-core/net/net.c b/grub-core/net/net.c index 2b6771523..9f09f8e48 100644 --- a/grub-core/net/net.c +++ b/grub-core/net/net.c @@ -1521,7 +1521,8 @@ grub_net_fs_close (grub_file_t file) grub_netbuff_free (file->device->net->packs.first->nb); grub_net_remove_packet (file->device->net->packs.first); } - file->device->net->protocol->close (file); + if (!file->device->net->broken) + file->device->net->protocol->close (file); grub_free (file->device->net->name); return GRUB_ERR_NONE; } @@ -1744,7 +1745,10 @@ grub_net_seek_real (struct grub_file *file, grub_off_t offset) file->device->net->stall = 0; err = file->device->net->protocol->open (file, file->device->net->name); if (err) - return err; + { + file->device->net->broken = 1; + return err; + } grub_net_fs_read_real (file, NULL, offset); return grub_errno; } @@ -1753,6 +1757,9 @@ grub_net_seek_real (struct grub_file *file, grub_off_t offset) static grub_ssize_t grub_net_fs_read (grub_file_t file, char *buf, grub_size_t len) { + if (file->device->net->broken) + return -1; + if (file->offset != file->device->net->offset) { grub_err_t err; diff --git a/grub-core/net/tftp.c b/grub-core/net/tftp.c index ebbafe7a1..ee305e18a 100644 --- a/grub-core/net/tftp.c +++ b/grub-core/net/tftp.c @@ -400,6 +400,7 @@ tftp_open (struct grub_file *file, const char *filename) { grub_net_udp_close (data->sock); grub_free (data); + file->data = NULL; return grub_errno; } diff --git a/include/grub/net.h b/include/grub/net.h index db21e792f..a64a04cc8 100644 --- a/include/grub/net.h +++ b/include/grub/net.h @@ -276,6 +276,7 @@ typedef struct grub_net grub_fs_t fs; int eof; int stall; + int broken; } *grub_net_t; extern grub_net_t (*EXPORT_VAR (grub_net_open)) (const char *name); |