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author | Taylor Blau <me@ttaylorr.com> | 2023-04-06 14:07:58 -0400 |
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committer | Johannes Schindelin <johannes.schindelin@gmx.de> | 2023-04-17 21:15:40 +0200 |
commit | a5bb10fd5e74101e7c07da93e7c32bbe60f6173a (patch) | |
tree | abd52d3a55253bb7d2c58dbd1e58749030c18988 /config.c | |
parent | 29198213c9163c1d552ee2bdbf78d2b09ccc98b8 (diff) | |
download | git-a5bb10fd5e74101e7c07da93e7c32bbe60f6173a.tar.gz |
config: avoid fixed-sized buffer when renaming/deleting a section
When renaming (or deleting) a section of configuration, Git uses the
function `git_config_copy_or_rename_section_in_file()` to rewrite the
configuration file after applying the rename or deletion to the given
section.
To do this, Git repeatedly calls `fgets()` to read the existing
configuration data into a fixed size buffer.
When the configuration value under `old_name` exceeds the size of the
buffer, we will call `fgets()` an additional time even if there is no
newline in the configuration file, since our read length is capped at
`sizeof(buf)`.
If the first character of the buffer (after zero or more characters
satisfying `isspace()`) is a '[', Git will incorrectly treat it as
beginning a new section when the original section is being removed. In
other words, a configuration value satisfying this criteria can
incorrectly be considered as a new secftion instead of a variable in the
original section.
Avoid this issue by using a variable-width buffer in the form of a
strbuf rather than a fixed-with region on the stack. A couple of small
points worth noting:
- Using a strbuf will cause us to allocate arbitrary sizes to match
the length of each line. In practice, we don't expect any
reasonable configuration files to have lines that long, and a
bandaid will be introduced in a later patch to ensure that this is
the case.
- We are using strbuf_getwholeline() here instead of strbuf_getline()
in order to match `fgets()`'s behavior of leaving the trailing LF
character on the buffer (as well as a trailing NUL).
This could be changed later, but using strbuf_getwholeline() changes
the least about this function's implementation, so it is picked as
the safest path.
- It is temping to want to replace the loop to skip over characters
matching isspace() at the beginning of the buffer with a convenience
function like `strbuf_ltrim()`. But this is the wrong approach for a
couple of reasons:
First, it involves a potentially large and expensive `memmove()`
which we would like to avoid. Second, and more importantly, we also
*do* want to preserve those spaces to avoid changing the output of
other sections.
In all, this patch is a minimal replacement of the fixed-width buffer in
`git_config_copy_or_rename_section_in_file()` to instead use a `struct
strbuf`.
Reported-by: André Baptista <andre@ethiack.com>
Reported-by: Vítor Pinho <vitor@ethiack.com>
Helped-by: Patrick Steinhardt <ps@pks.im>
Co-authored-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Diffstat (limited to 'config.c')
-rw-r--r-- | config.c | 13 |
1 files changed, 7 insertions, 6 deletions
@@ -3091,7 +3091,7 @@ static int git_config_copy_or_rename_section_in_file(const char *config_filename char *filename_buf = NULL; struct lock_file lock = LOCK_INIT; int out_fd; - char buf[1024]; + struct strbuf buf = STRBUF_INIT; FILE *config_file = NULL; struct stat st; struct strbuf copystr = STRBUF_INIT; @@ -3132,14 +3132,14 @@ static int git_config_copy_or_rename_section_in_file(const char *config_filename goto out; } - while (fgets(buf, sizeof(buf), config_file)) { + while (!strbuf_getwholeline(&buf, config_file, '\n')) { unsigned i; int length; int is_section = 0; - char *output = buf; - for (i = 0; buf[i] && isspace(buf[i]); i++) + char *output = buf.buf; + for (i = 0; buf.buf[i] && isspace(buf.buf[i]); i++) ; /* do nothing */ - if (buf[i] == '[') { + if (buf.buf[i] == '[') { /* it's a section */ int offset; is_section = 1; @@ -3158,7 +3158,7 @@ static int git_config_copy_or_rename_section_in_file(const char *config_filename strbuf_reset(©str); } - offset = section_name_match(&buf[i], old_name); + offset = section_name_match(&buf.buf[i], old_name); if (offset > 0) { ret++; if (new_name == NULL) { @@ -3233,6 +3233,7 @@ out: out_no_rollback: free(filename_buf); config_store_data_clear(&store); + strbuf_release(&buf); return ret; } |