Fix builtin-fetch memory corruption by not overstepping array
PATCH RESEND 1/2 Fix builtin-fetch memory corruption by not overstepping array
A long time ago Junio added this line to always ensure that the output array created by remove_duplicates() had a NULL as its terminating node. Today none of the downstream consumers of this array care about a NULL terminator; they only pay attention to the size of the array (as indicated by nr_heads). In (nearly?) all cases passing a NULL element will cause SIGSEGV failures. So this NULL terminal is not actually necessary.
Unfortunately we cannot continue to NULL terminate the array at this point as the array may only have been allocated large enough to match the input of nr_heads. If there are no duplicates than we would be trying to store NULL into heads[nr_heads] and that may be outside of the array.
My recent series to cleanup builtin-fetch changed the allocation of the heads array from 256 entries to exactly nr_heads thus ensuring we were always overstepping the array and causing memory corruption.
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*** RESEND TO CORRECT FROM+SBO ***
Sorry Junio. I realized too late that the headers were wrong. That's what I get for not configuring ~/.gitconfig on my amd64 Linux box. ;-)
builtin-fetch-pack.c | 1 - 1 files changed, 0 insertions(+), 1 deletions(-)
builtin-fetch-pack.c +0 -1
@@ -654,7 +654,6 @@ static int remove_duplicates(int nr_heads, char **heads) heads[dst] = heads[src]; dst++; } - heads[dst] =0 ;return dst; }
Signature · 1 line
1.5.3.1.921.g8c3b
Quoted 5 lines · Shawn O. Pearce
Unfortunately we cannot continue to NULL terminate the array at this point as the array may only have been allocated large enough to match the input of
nr_heads. If there are no duplicates than we would be trying to store NULL into heads[nr_heads] and that may be outside of the array.
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builtin-fetch-pack.c static int remove_duplicates(int nr_heads, char **heads) · line 659
Quoted 12 lines
builtin-fetch-pack.c +0
-1@@ -654,7 +654,6 @@ static int remove_duplicates(int nr_heads, char **heads) heads[dst] = heads[src]; dst++; } - heads[dst] =0 ;return dst; }
This fortunately does not appear to be a bug in maint, master, or next. It appears to be isolated to the builtin-fetch topic. The builtin-fetch topic changed fetch-pack to be builtin-fetch-pack and in doing so changed things such that the heads array might not have room for this final entry.
In maint/master/next the heads array is actually backed by the argv passed into main by the kernel, and that does have an existing NULL terminator, which the above "heads[dst] = 0" is simply going to overwrite if "heads == nr_heads".
Signature · 1 line
Shawn.
Quoted 5 lines · Shawn O. Pearce
*** RESEND TO CORRECT FROM+SBO ***
Sorry Junio. I realized too late that the headers were wrong. That's what I get for not configuring ~/.gitconfig on my amd64 Linux box. ;-)
Actually this might have been a good thing, according to Linus. It is an evidence that you built and tested that change on the "blink" box not your usual box.