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fix: invalid buffer size argument to snprintf #22729

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Problem:
Crash in findtags_add_match with FORTIFY_SOURCE=3.
Note: Fedora 38 packages are now built with -D_FORTIFY_SOURCE=3 by default.
1. Compile with overflow protection.
2. nvim --clean
3. :h <Space> <Tab>
4. `*** overflow detected ***: terminated`

The additional checks for the stated buffer size and the actual bounds
of the buffer do not match. See `___snprintf_chk` in the glibc sources:
https://sourceware.org/git/?p=glibc.git;a=blob;f=debug/snprintf_chk.c;h=59577de076c570b81307dd31c8c73e265808cf4c;hb=HEAD#l28

Solution:
Fix arithmetic error: The length of the previously written data is now
subtracted from the total size of the buffer, instead of added on top.

close #22718
This commit is contained in:
koeleck 2023-03-19 22:32:37 +01:00 committed by GitHub
parent ecc4d0e435
commit 84027f7515
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GPG Key ID: 4AEE18F83AFDEB23
1 changed files with 4 additions and 2 deletions
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6
src/nvim/tag.c
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@ -1947,6 +1947,7 @@ static void findtags_add_match(findtags_state_T *st, tagptrs_T *tagpp, findtags_
const bool name_only = (st->flags & TAG_NAMES);
int mtt;
size_t len = 0;
size_t mfp_size = 0;
bool is_current; // file name matches
bool is_static; // current tag line is static
char *mfp;
@ -1990,13 +1991,14 @@ static void findtags_add_match(findtags_state_T *st, tagptrs_T *tagpp, findtags_
// The format is {tagname}@{lang}NUL{heuristic}NUL
*tagpp->tagname_end = NUL;
len = (size_t)(tagpp->tagname_end - tagpp->tagname);
mfp = xmalloc(sizeof(char) + len + 10 + ML_EXTRA + 1);
mfp_size = sizeof(char) + len + 10 + ML_EXTRA + 1;
mfp = xmalloc(mfp_size);
p = mfp;
STRCPY(p, tagpp->tagname);
p[len] = '@';
STRCPY(p + len + 1, st->help_lang);
snprintf(p + len + 1 + ML_EXTRA, strlen(p) + len + 1 + ML_EXTRA, "%06d",
snprintf(p + len + 1 + ML_EXTRA, mfp_size - (len + 1 + ML_EXTRA), "%06d",
help_heuristic(tagpp->tagname,
margs->match_re ? margs->matchoff : 0,
!margs->match_no_ic) + st->help_pri);