[PATCH] ubifs: Fix lockup/crash when reading files

[Pali Rohár]

On Thursday 19 May 2022 10:04:31 Pali Rohár wrote:
> On Thursday 19 May 2022 07:01:19 Stefan Roese wrote:
> > On 17.05.22 22:45, Pali Rohár wrote:
> > > Commit b1a14f8a1c2e ("UBIFS: Change ubifsload to not read beyond the
> > > requested size") added optimization to do not read more bytes than it is
> > > really needed. But this commit introduced incorrect handling of the hole at
> > > the end of file. This logic cause U-Boot to crash or lockup when trying to
> > > read from the ubifs filesystem.
> > > 
> > > When read_block() call returns -ENOENT error (not an error, but the hole)
> > > then dn-> structure is not filled and contain garbage. So using of dn->size
> > > for memcpy() argument cause that U-Boot tries to copy unspecified amount of
> > > bytes from possible unmapped memory. Which randomly cause lockup of P2020
> > > CPU.
> > > 
> > > Fix this issue by copying UBIFS_BLOCK_SIZE bytes from read buffer when
> > > dn->size is not available. UBIFS_BLOCK_SIZE is the size of the buffer
> > > itself and read_block() fills buffer by zeros when it returns -ENOENT.
> > > 
> > > This patch fixes ubifsload on P2020.
> > > 
> > > Fixes: b1a14f8a1c2e ("UBIFS: Change ubifsload to not read beyond the requested size")
> > > Signed-off-by: Pali Rohár <pali at kernel.org>
> > 
> > Reviewed-by: Stefan Roese <sr at denx.de>

Anyway, who is maintainer of fs / ubifs code and can take this bugfix patch?

> > 
> > > ---
> > > 
> > > Stefan, could you please look at this patch? Mentioned commit was
> > > introduced by you more than 11 years ago. I'm surprised that nobody hit
> > > this issue yet, but it looks like older U-Boot versions somehow filled
> > > small garbage number into dn->size and did not cause U-Boot
> > > lockup/crash.
> > 
> > So long ago. I don't really remember the details. IIRC, I introduced the
> > UBIFS support for some MIPS based board at that time. My best assumption
> > is, that UBIFS is rarely used in U-Boot in general.
> 
> It is used on Turris 1.x (powerpc).
> 
> > Thanks,
> > Stefan
> > 
> > > ---
> > >   fs/ubifs/ubifs.c | 2 ++
> > >   1 file changed, 2 insertions(+)
> > > 
> > > diff --git a/fs/ubifs/ubifs.c b/fs/ubifs/ubifs.c
> > > index d6be5c947d7e..d3026e310168 100644
> > > --- a/fs/ubifs/ubifs.c
> > > +++ b/fs/ubifs/ubifs.c
> > > @@ -771,40 +771,42 @@ static int do_readpage(struct ubifs_info *c, struct inode *inode,
> > >   				buff = malloc_cache_aligned(UBIFS_BLOCK_SIZE);
> > >   				if (!buff) {
> > >   					printf("%s: Error, malloc fails!\n",
> > >   					       __func__);
> > >   					err = -ENOMEM;
> > >   					break;
> > >   				}
> > >   				/* Read block-size into temp buffer */
> > >   				ret = read_block(inode, buff, block, dn);
> > >   				if (ret) {
> > >   					err = ret;
> > >   					if (err != -ENOENT) {
> > >   						free(buff);
> > >   						break;
> > >   					}
> > >   				}
> > >   				if (last_block_size)
> > >   					dlen = last_block_size;
> > > +				else if (ret)
> > > +					dlen = UBIFS_BLOCK_SIZE;
> > >   				else
> > >   					dlen = le32_to_cpu(dn->size);
> > >   				/* Now copy required size back to dest */
> > >   				memcpy(addr, buff, dlen);
> > >   				free(buff);
> > >   			} else {
> > >   				ret = read_block(inode, addr, block, dn);
> > >   				if (ret) {
> > >   					err = ret;
> > >   					if (err != -ENOENT)
> > >   						break;
> > >   				}
> > >   			}
> > >   		}
> > >   		if (++i >= UBIFS_BLOCKS_PER_PAGE)
> > >   			break;
> > >   		block += 1;
> > >   		addr += UBIFS_BLOCK_SIZE;
> > 
> > Viele Grüße,
> > Stefan Roese
> > 
> > -- 
> > DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
> > HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
> > Phone: (+49)-8142-66989-51 Fax: (+49)-8142-66989-80 Email: sr at denx.de