[PATCH] fs/squashfs: sqfs_read: Prevent arbitrary code execution

[Tom Rini]

On Tue, Jun 07, 2022 at 06:00:38PM +0800, Jincheng Wang wrote:

> It works well, thanks for your work.

Can you please provide a Tested-by?  Thanks!

> 
> 
> Miquel Raynal <miquel.raynal at bootlin.com> 于2022年6月3日周五 23:26写道：
> >
> > Following Jincheng's report, an out-of-band write leading to arbitrary
> > code execution is possible because on one side the squashfs logic
> > accepts directory names up to 65535 bytes (u16), while U-Boot fs logic
> > accepts directory names up to 255 bytes long.
> >
> > Prevent such an exploit from happening by capping directory name sizes
> > to 255. Use a define for this purpose so that developers can link the
> > limitation to its source and eventually kill it some day by dynamically
> > allocating this array (if ever desired).
> >
> > Link: https://lore.kernel.org/all/CALO=DHFB+yBoXxVr5KcsK0iFdg+e7ywko4-e+72kjbcS8JBfPw@mail.gmail.com
> > Reported-by: Jincheng Wang <jc.w4ng at gmail.com>
> > Signed-off-by: Miquel Raynal <miquel.raynal at bootlin.com>
> > ---
> >
> > Hello Jincheng, can you please give this fix a try?
> >
> > Thanks!
> > Miquèl
> >
> >  fs/squashfs/sqfs.c | 8 +++++---
> >  include/fs.h       | 4 +++-
> >  2 files changed, 8 insertions(+), 4 deletions(-)
> >
> > diff --git a/fs/squashfs/sqfs.c b/fs/squashfs/sqfs.c
> > index b4484fa17f5..ee6ac8b3e4d 100644
> > --- a/fs/squashfs/sqfs.c
> > +++ b/fs/squashfs/sqfs.c
> > @@ -976,6 +976,7 @@ int sqfs_readdir(struct fs_dir_stream *fs_dirs, struct fs_dirent **dentp)
> >         int i_number, offset = 0, ret;
> >         struct fs_dirent *dent;
> >         unsigned char *ipos;
> > +       u16 name_size;
> >
> >         dirs = (struct squashfs_dir_stream *)fs_dirs;
> >         if (!dirs->size) {
> > @@ -1058,9 +1059,10 @@ int sqfs_readdir(struct fs_dir_stream *fs_dirs, struct fs_dirent **dentp)
> >                 return -SQFS_STOP_READDIR;
> >         }
> >
> > -       /* Set entry name */
> > -       strncpy(dent->name, dirs->entry->name, dirs->entry->name_size + 1);
> > -       dent->name[dirs->entry->name_size + 1] = '\0';
> > +       /* Set entry name (capped at FS_DIRENT_NAME_LEN which is a U-Boot limitation) */
> > +       name_size = min_t(u16, dirs->entry->name_size, FS_DIRENT_NAME_LEN - 1);
> > +       strncpy(dent->name, dirs->entry->name, name_size);
> > +       dent->name[name_size] = '\0';
> >
> >         offset = dirs->entry->name_size + 1 + SQFS_ENTRY_BASE_LENGTH;
> >         dirs->entry_count--;
> > diff --git a/include/fs.h b/include/fs.h
> > index b43f16a692f..2195dc172ec 100644
> > --- a/include/fs.h
> > +++ b/include/fs.h
> > @@ -174,6 +174,8 @@ int fs_write(const char *filename, ulong addr, loff_t offset, loff_t len,
> >  #define FS_DT_REG  8         /* regular file */
> >  #define FS_DT_LNK  10        /* symbolic link */
> >
> > +#define FS_DIRENT_NAME_LEN 256
> > +
> >  /**
> >   * struct fs_dirent - directory entry
> >   *
> > @@ -194,7 +196,7 @@ struct fs_dirent {
> >         /** change_time:        time of last modification */
> >         struct rtc_time change_time;
> >         /** name:               file name */
> > -       char name[256];
> > +       char name[FS_DIRENT_NAME_LEN];
> >  };
> >
> >  /* Note: fs_dir_stream should be treated as opaque to the user of fs layer */
> > --
> > 2.34.1
> >

-- 
Tom
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