Ziplists had a bug that was discovered while investigating a different
issue, resulting in a corrupted ziplist representation, and a likely
segmentation foult and/or data corruption of the last element of the
ziplist, once the ziplist is accessed again.
The bug happens when a specific set of insertions / deletions is
performed so that an entry is encoded to have a "prevlen" field (the
length of the previous entry) of 5 bytes but with a count that could be
encoded in a "prevlen" field of a since byte. This could happen when the
"cascading update" process called by ziplistInsert()/ziplistDelete() in
certain contitious forces the prevlen to be bigger than necessary in
order to avoid too much data moving around.
Once such an entry is generated, inserting a very small entry
immediately before it will result in a resizing of the ziplist for a
count smaller than the current ziplist length (which is a violation,
inserting code expects the ziplist to get bigger actually). So an FF
byte is inserted in a misplaced position. Moreover a realloc() is
performed with a count smaller than the ziplist current length so the
final bytes could be trashed as well.
SECURITY IMPLICATIONS:
Currently it looks like an attacker can only crash a Redis server by
providing specifically choosen commands. However a FF byte is written
and there are other memory operations that depend on a wrong count, so
even if it is not immediately apparent how to mount an attack in order
to execute code remotely, it is not impossible at all that this could be
done. Attacks always get better... and we did not spent enough time in
order to think how to exploit this issue, but security researchers
or malicious attackers could.
Ziplists had a bug that was discovered while investigating a different
issue, resulting in a corrupted ziplist representation, and a likely
segmentation foult and/or data corruption of the last element of the
ziplist, once the ziplist is accessed again.
The bug happens when a specific set of insertions / deletions is
performed so that an entry is encoded to have a "prevlen" field (the
length of the previous entry) of 5 bytes but with a count that could be
encoded in a "prevlen" field of a since byte. This could happen when the
"cascading update" process called by ziplistInsert()/ziplistDelete() in
certain contitious forces the prevlen to be bigger than necessary in
order to avoid too much data moving around.
Once such an entry is generated, inserting a very small entry
immediately before it will result in a resizing of the ziplist for a
count smaller than the current ziplist length (which is a violation,
inserting code expects the ziplist to get bigger actually). So an FF
byte is inserted in a misplaced position. Moreover a realloc() is
performed with a count smaller than the ziplist current length so the
final bytes could be trashed as well.
SECURITY IMPLICATIONS:
Currently it looks like an attacker can only crash a Redis server by
providing specifically choosen commands. However a FF byte is written
and there are other memory operations that depend on a wrong count, so
even if it is not immediately apparent how to mount an attack in order
to execute code remotely, it is not impossible at all that this could be
done. Attacks always get better... and we did not spent enough time in
order to think how to exploit this issue, but security researchers
or malicious attackers could.
This header file is for libs, like ziplist.c, that we want to leave
almost separted from the core. The panic() calls will be easy to delete
in order to use such files outside, but the debugging info we gain are
very valuable compared to simple assertions where it is not possible to
print debugging info.
This header file is for libs, like ziplist.c, that we want to leave
almost separted from the core. The panic() calls will be easy to delete
in order to use such files outside, but the debugging info we gain are
very valuable compared to simple assertions where it is not possible to
print debugging info.
This is of great interest because allows us to print debugging
informations that could be of useful when debugging, like in the
following example:
serverPanic("Unexpected encoding for object %d, %d",
obj->type, obj->encoding);
This is of great interest because allows us to print debugging
informations that could be of useful when debugging, like in the
following example:
serverPanic("Unexpected encoding for object %d, %d",
obj->type, obj->encoding);
Don't go over 80 cols. Start with captial letter, capital letter afer
point, end comment with a point and so forth. No actual code behavior
touched at all.
Don't go over 80 cols. Start with captial letter, capital letter afer
point, end comment with a point and so forth. No actual code behavior
touched at all.
