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

[Pali Rohár]

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>
> 
> > ---
> > 
> > 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
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