On Wed, Feb 05, 2020 at 10:40:31PM -0700, Simon Glass wrote:
> Allow enabling ASSUME_VALID_INPUT to disable sanity checks on the device
> tree and the parameters to libfdt. This assumption covers that cases where
> the problem could be with either.
>
> Signed-off-by: Simon Glass <sjg@xxxxxxxxxxxx>
> ---
>
> Changes in v5:
> - Include just VALID_INPUT checks in this patch
>
> Changes in v4: None
> Changes in v3: None
> Changes in v2: None
>
> libfdt/fdt.c | 12 +++++----
> libfdt/fdt_ro.c | 71 ++++++++++++++++++++++++++++++++-----------------
> 2 files changed, 54 insertions(+), 29 deletions(-)
>
> diff --git a/libfdt/fdt.c b/libfdt/fdt.c
> index 03f2b7d..e2c1da0 100644
> --- a/libfdt/fdt.c
> +++ b/libfdt/fdt.c
> @@ -126,10 +126,11 @@ const void *fdt_offset_ptr(const void *fdt, int offset, unsigned int len)
> {
> unsigned absoffset = offset + fdt_off_dt_struct(fdt);
>
> - if ((absoffset < offset)
> - || ((absoffset + len) < absoffset)
> - || (absoffset + len) > fdt_totalsize(fdt))
> - return NULL;
> + if (!can_assume(VALID_INPUT))
> + if ((absoffset < offset)
> + || ((absoffset + len) < absoffset)
> + || (absoffset + len) > fdt_totalsize(fdt))
> + return NULL;
>
> if (fdt_version(fdt) >= 0x11)
> if (((offset + len) < offset)
> @@ -185,7 +186,8 @@ uint32_t fdt_next_tag(const void *fdt, int startoffset, int *nextoffset)
> return FDT_END;
> }
>
> - if (!fdt_offset_ptr(fdt, startoffset, offset - startoffset))
> + if (!can_assume(VALID_INPUT) &&
> + !fdt_offset_ptr(fdt, startoffset, offset - startoffset))
> return FDT_END; /* premature end */
>
> *nextoffset = FDT_TAGALIGN(offset);
> diff --git a/libfdt/fdt_ro.c b/libfdt/fdt_ro.c
> index b41083f..07c13c9 100644
> --- a/libfdt/fdt_ro.c
> +++ b/libfdt/fdt_ro.c
> @@ -16,7 +16,7 @@ static int fdt_nodename_eq_(const void *fdt, int offset,
> int olen;
> const char *p = fdt_get_name(fdt, offset, &olen);
>
> - if (!p || olen < len)
> + if (!p || (!can_assume(VALID_INPUT) && olen < len))
Oof, this one's subtle. We certainly *can* have olen < len even in
perfectly valid cases. However, if we're assuming validly \0
terminated strings in the strings block *and* no \0s in s (which you
can with assume(VALID_INPUT)), then the memcmp() will necessarily pick
up that case.
If we also assume memcmp() is the obvious byte-by-byte implementation
then it will stop before accessing beyond the end of the strings block
string. But... I don't think that's necessarily the case for all C
libraries / runtimes. So, if this is close to the end of the strings
block, the memcmp() could access beyond the dtb buffer, which is a no
no.
Now, I guess we could have an assume(DUMB_MEMCMP) and/or
assume(READ_ACCESS_SLIGHTLY_BEYOND_THE_DTB_WILL_WORK), but we're
getting really esoteric now.
Is avoiding this one comparison worth it?
> /* short match */
> return 0;
>
> @@ -33,17 +33,26 @@ static int fdt_nodename_eq_(const void *fdt, int offset,
>
> const char *fdt_get_string(const void *fdt, int stroffset, int *lenp)
> {
> - int32_t totalsize = fdt_ro_probe_(fdt);
> - uint32_t absoffset = stroffset + fdt_off_dt_strings(fdt);
> + int32_t totalsize;
> + uint32_t absoffset;
> size_t len;
> int err;
> const char *s, *n;
>
> + if (can_assume(VALID_INPUT)) {
> + s = (const char *)fdt + fdt_off_dt_strings(fdt) + stroffset;
> +
> + if (lenp)
> + *lenp = strlen(s);
> + return s;
> + }
> + totalsize = fdt_ro_probe_(fdt);
> err = totalsize;
> if (totalsize < 0)
> goto fail;
>
> err = -FDT_ERR_BADOFFSET;
> + absoffset = stroffset + fdt_off_dt_strings(fdt);
> if (absoffset >= totalsize)
> goto fail;
> len = totalsize - absoffset;
> @@ -151,10 +160,13 @@ static const struct fdt_reserve_entry *fdt_mem_rsv(const void *fdt, int n)
> int offset = n * sizeof(struct fdt_reserve_entry);
> int absoffset = fdt_off_mem_rsvmap(fdt) + offset;
>
> - if (absoffset < fdt_off_mem_rsvmap(fdt))
> - return NULL;
> - if (absoffset > fdt_totalsize(fdt) - sizeof(struct fdt_reserve_entry))
> - return NULL;
> + if (!can_assume(VALID_INPUT)) {
> + if (absoffset < fdt_off_mem_rsvmap(fdt))
> + return NULL;
> + if (absoffset > fdt_totalsize(fdt) -
> + sizeof(struct fdt_reserve_entry))
> + return NULL;
> + }
> return fdt_mem_rsv_(fdt, n);
> }
>
> @@ -164,7 +176,7 @@ int fdt_get_mem_rsv(const void *fdt, int n, uint64_t *address, uint64_t *size)
>
> FDT_RO_PROBE(fdt);
> re = fdt_mem_rsv(fdt, n);
> - if (!re)
> + if (!can_assume(VALID_INPUT) && !re)
> return -FDT_ERR_BADOFFSET;
>
> *address = fdt64_ld(&re->address);
> @@ -292,8 +304,9 @@ const char *fdt_get_name(const void *fdt, int nodeoffset, int *len)
> if (!can_assume(VALID_DTB)) {
> if ((err = fdt_ro_probe_(fdt)) < 0)
> goto fail;
> - if ((err = fdt_check_node_offset_(fdt, nodeoffset)) < 0)
> - goto fail;
> + if (can_assume(VALID_INPUT) &&
That should be !can_assume, no?
> + (err = fdt_check_node_offset_(fdt, nodeoffset)) < 0)
> + goto fail;
> }
>
> nameptr = nh->name;
> @@ -349,7 +362,8 @@ static const struct fdt_property *fdt_get_property_by_offset_(const void *fdt,
> int err;
> const struct fdt_property *prop;
>
> - if ((err = fdt_check_prop_offset_(fdt, offset)) < 0) {
> + if (!can_assume(VALID_INPUT) &&
> + (err = fdt_check_prop_offset_(fdt, offset)) < 0) {
> if (lenp)
> *lenp = err;
> return NULL;
> @@ -391,7 +405,8 @@ static const struct fdt_property *fdt_get_property_namelen_(const void *fdt,
> (offset = fdt_next_property_offset(fdt, offset))) {
> const struct fdt_property *prop;
>
> - if (!(prop = fdt_get_property_by_offset_(fdt, offset, lenp))) {
> + prop = fdt_get_property_by_offset_(fdt, offset, lenp);
> + if (!can_assume(VALID_INPUT) && !prop) {
> offset = -FDT_ERR_INTERNAL;
So, arguably you could put this one under a weaker assumption flag.
Basicaly FDT_ERR_INTERNAL errors should *never* happen, even with bad
input - they're basically assert()s, except I didn't want to rely on
the runtime things that assert() needs.
> break;
> }
> @@ -464,14 +479,19 @@ const void *fdt_getprop_by_offset(const void *fdt, int offset,
> if (namep) {
> const char *name;
> int namelen;
> - name = fdt_get_string(fdt, fdt32_ld(&prop->nameoff),
> - &namelen);
> - if (!name) {
> - if (lenp)
> - *lenp = namelen;
> - return NULL;
> +
> + if (!can_assume(VALID_INPUT)) {
> + name = fdt_get_string(fdt, fdt32_ld(&prop->nameoff),
> + &namelen);
> + if (!name) {
> + if (lenp)
> + *lenp = namelen;
> + return NULL;
> + }
> + *namep = name;
> + } else {
> + *namep = fdt_string(fdt, fdt32_ld(&prop->nameoff));
> }
> - *namep = name;
> }
>
> /* Handle realignment */
> @@ -601,10 +621,12 @@ int fdt_supernode_atdepth_offset(const void *fdt, int nodeoffset,
> }
> }
>
> - if ((offset == -FDT_ERR_NOTFOUND) || (offset >= 0))
> - return -FDT_ERR_BADOFFSET;
> - else if (offset == -FDT_ERR_BADOFFSET)
> - return -FDT_ERR_BADSTRUCTURE;
> + if (!can_assume(VALID_INPUT)) {
> + if ((offset == -FDT_ERR_NOTFOUND) || (offset >= 0))
> + return -FDT_ERR_BADOFFSET;
> + else if (offset == -FDT_ERR_BADOFFSET)
> + return -FDT_ERR_BADSTRUCTURE;
> + }
>
> return offset; /* error from fdt_next_node() */
> }
> @@ -616,7 +638,8 @@ int fdt_node_depth(const void *fdt, int nodeoffset)
>
> err = fdt_supernode_atdepth_offset(fdt, nodeoffset, 0, &nodedepth);
> if (err)
> - return (err < 0) ? err : -FDT_ERR_INTERNAL;
> + return (can_assume(VALID_INPUT) || err < 0) ? err :
> + -FDT_ERR_INTERNAL;
> return nodedepth;
> }
>
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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