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auto-fix bin/sbin duplicates #159

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f4eab6f
bump fedora used in mkosi to rawhide
lnykryn Nov 7, 2025
8d6d448
alternatives: refactor state management and auto-fix bin/sbin duplicates
lnykryn Nov 7, 2025
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156 changes: 150 additions & 6 deletions alternatives.c
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Original file line number Diff line number Diff line change
Expand Up @@ -337,8 +337,84 @@ void nextLine(char **buf, char **line) {
*line = parseLine(buf);
}

static int readConfig(struct alternativeSet *set, const char *title,
const char *altDir, const char *stateDir, int flags) {
/* Forward declaration */
static int writeStateConf(struct alternativeSet *set, const char *stateDir, int flags);

/*
* Detect and remove bin/sbin duplicate alternatives.
* Returns the number of duplicates removed.
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Copilot AI Nov 13, 2025

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The function comment states "Returns the number of duplicates removed" but doesn't document important behavior:

  • The function modifies the alternativeSet in place
  • It may adjust the best and current indices
  • It prefers keeping alternatives with paths NOT containing /sbin/
  • Only operates when MERGED_SBIN is enabled

Consider expanding the documentation:

/*
 * Detect and remove bin/sbin duplicate alternatives.
 * 
 * When MERGED_SBIN is enabled, this function identifies alternatives that differ
 * only in bin vs sbin paths and removes duplicates, preferring to keep alternatives
 * with /bin/ paths over /sbin/ paths.
 * 
 * The function modifies the set in place, removing duplicate entries and adjusting
 * the best and current indices as needed.
 *
 * Returns: The number of duplicates removed, or 0 if MERGED_SBIN is not enabled.
 */
Suggested change
* Returns the number of duplicates removed.
*
* When MERGED_SBIN is enabled, this function identifies alternatives that differ
* only in bin vs sbin paths and removes duplicates, preferring to keep alternatives
* with /bin/ paths over /sbin/ paths.
*
* The function modifies the set in place, removing duplicate entries and adjusting
* the best and current indices as needed.
*
* Returns: The number of duplicates removed, or 0 if MERGED_SBIN is not enabled.

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*/
static int removeBinSbinDuplicates(struct alternativeSet *set, int flags) {
int i, j;
int removedCount = 0;

if (!MERGED_SBIN || set->numAlts < 2)
return 0;

for (i = 0; i < set->numAlts; i++) {
for (j = i + 1; j < set->numAlts; j++) {
/* Check if they differ only in bin/sbin (or are exactly the same) */
if (streq_bin(set->alts[i].leader.target, set->alts[j].leader.target)) {
int k;

/* Check if all followers match */
for (k = 0; k < set->alts[i].numFollowers; k++) {
if (!streq_bin(set->alts[i].followers[k].target,
set->alts[j].followers[k].target))
break;
}
Comment on lines +360 to +365
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This code assumes both alternatives have the same number of followers without checking. If set->alts[j].numFollowers differs from set->alts[i].numFollowers, this will either miss followers or access memory out of bounds.

Add a check before the loop:

/* Check if they have the same number of followers */
if (set->alts[i].numFollowers != set->alts[j].numFollowers)
    continue;

/* Check if all followers match */
for (k = 0; k < set->alts[i].numFollowers; k++) {

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/* If any follower didn't match, skip this pair */
if (k < set->alts[i].numFollowers)
continue;

/* Keep i if it is not in /sbin/, otherwise keep j */
if (strstr(set->alts[i].leader.target, "/sbin/")) {
if (FL_VERBOSE(flags)) {
fprintf(stderr, _("removing duplicate alternative: %s (keeping %s)\n"),
set->alts[i].leader.target, set->alts[j].leader.target);
}
clearAlternative(&set->alts[i]);
set->alts[i] = set->alts[j];
if (set->best == j)
set->best = i;
if (set->current == j)
set->current = i;
} else {
if (FL_VERBOSE(flags)) {
fprintf(stderr, _("removing duplicate alternative: %s (keeping %s)\n"),
set->alts[j].leader.target, set->alts[i].leader.target);
}
clearAlternative(&set->alts[j]);
}

/* Always remove j (shift everything down) */
for (int k = j; k < set->numAlts - 1; k++) {
set->alts[k] = set->alts[k + 1];
Comment on lines +391 to +392
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[nitpick] Variable k is declared within the nested if statement block (line 358), but it's used in the for loop (line 391) at the same nesting level. While this is valid C, the variable k in line 391 shadows the earlier declaration from line 358. This could be confusing.

Consider using a different variable name for the shift loop, such as idx or m, to avoid shadowing:

for (int m = j; m < set->numAlts - 1; m++) {
    set->alts[m] = set->alts[m + 1];
}
Suggested change
for (int k = j; k < set->numAlts - 1; k++) {
set->alts[k] = set->alts[k + 1];
for (int m = j; m < set->numAlts - 1; m++) {
set->alts[m] = set->alts[m + 1];

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}
set->numAlts--;
removedCount++;

/* Adjust current and best indices if they're after j */
if (set->current > j)
set->current--;
if (set->best > j)
set->best--;

/* Adjust j since we removed an element */
j--;
Comment on lines +382 to +404
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Copilot AI Nov 13, 2025

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There's a logic error in this branch. When set->alts[i] is in /sbin/, the code:

  1. Clears set->alts[i]
  2. Copies set->alts[j] to set->alts[i]
  3. Then at line 391-393, shifts all elements from j down, overwriting set->alts[j]

This means set->alts[i] now contains a shallow copy of data that was just shifted/moved. Since clearAlternative was already called on the original set->alts[i], and set->alts[j] is being moved (not copied), this creates a double-free risk.

The fix is to NOT shift when keeping j's value in i. The removal should only happen in the else branch. The code should be restructured to:

  • Identify which alternative to remove (either i or j)
  • Clear that alternative
  • If removing i, move j to i's position
  • Shift all elements after the removed index down
Suggested change
} else {
if (FL_VERBOSE(flags)) {
fprintf(stderr, _("removing duplicate alternative: %s (keeping %s)\n"),
set->alts[j].leader.target, set->alts[i].leader.target);
}
clearAlternative(&set->alts[j]);
}
/* Always remove j (shift everything down) */
for (int k = j; k < set->numAlts - 1; k++) {
set->alts[k] = set->alts[k + 1];
}
set->numAlts--;
removedCount++;
/* Adjust current and best indices if they're after j */
if (set->current > j)
set->current--;
if (set->best > j)
set->best--;
/* Adjust j since we removed an element */
j--;
/* Now remove j (which is now a duplicate of i) */
for (int k = j; k < set->numAlts - 1; k++) {
set->alts[k] = set->alts[k + 1];
}
set->numAlts--;
removedCount++;
/* Adjust current and best indices if they're after j */
if (set->current > j)
set->current--;
if (set->best > j)
set->best--;
/* Adjust j since we removed an element */
j--;
} else {
if (FL_VERBOSE(flags)) {
fprintf(stderr, _("removing duplicate alternative: %s (keeping %s)\n"),
set->alts[j].leader.target, set->alts[i].leader.target);
}
clearAlternative(&set->alts[j]);
for (int k = j; k < set->numAlts - 1; k++) {
set->alts[k] = set->alts[k + 1];
}
set->numAlts--;
removedCount++;
/* Adjust current and best indices if they're after j */
if (set->current > j)
set->current--;
if (set->best > j)
set->best--;
/* Adjust j since we removed an element */
j--;
}

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}
}
}

return removedCount;
}

/*
* Internal function to read alternatives configuration.
* Reads the config file and verifies symlinks without any modifications.
*/
static int readConfigInternal(struct alternativeSet *set, const char *title,
const char *altDir, const char *stateDir, int flags) {
char *path;
char *leader_path;
int fd;
Expand Down Expand Up @@ -587,6 +663,47 @@ static int readConfig(struct alternativeSet *set, const char *title,
return r;
}

/*
* Read alternatives configuration and remove bin/sbin duplicates if found.
* This is the main entry point for reading config.
*/
static int readConfig(struct alternativeSet *set, const char *title,
const char *altDir, const char *stateDir, int flags) {
int rc;

rc = readConfigInternal(set, title, altDir, stateDir, flags);
if (rc)
return rc;

/* If we removed duplicates, rewrite the config file and re-read */
if (removeBinSbinDuplicates(set, flags) > 0) {
if (FL_VERBOSE(flags))
fprintf(stderr, _("rewriting config after removing duplicates\n"));

if (!FL_TEST(flags)) {
rc = writeStateConf(set, stateDir, flags);
if (rc) {
fprintf(stderr, _("failed to write cleaned config for %s\n"), title);
return rc;
}

/* Free existing data before re-reading */
for (int i = 0; i < set->numAlts; i++) {
clearAlternative(&set->alts[i]);
}
free(set->alts);
free(set->currentLink);

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After freeing the data structures, the code re-reads the config into the same set structure. However, readConfigInternal initializes set->alts to NULL and set->numAlts to 0 (lines 436-437), but it doesn't reset other fields like set->mode, set->best, and set->current that may have been set during the first read. While readConfigInternal does set these fields (lines 438-440), there's a potential issue if the re-read fails partway through - the set would be in an inconsistent state.

Consider either:

  1. Memset the entire set structure to 0 before re-reading, or
  2. Move the initialization of all set fields to the very beginning of readConfigInternal
Suggested change
/* Zero out the set structure to avoid inconsistent state */
memset(set, 0, sizeof(*set));

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/* Re-read the config to ensure consistency */
rc = readConfigInternal(set, title, altDir, stateDir, flags);
if (rc)
return rc;
}
}

return 0;
}

static int isLink(char *path) {
struct stat sbuf;

Expand Down Expand Up @@ -706,15 +823,16 @@ static int makeLinks(struct linkSet *l, const char *altDir, int flags) {
return 0;
}

static int writeState(struct alternativeSet *set, const char *altDir,
const char *stateDir, int forceLinks, int flags) {
/*
* Write the alternatives configuration file to stateDir.
* This only updates the config file, not the actual symlinks.
*/
static int writeStateConf(struct alternativeSet *set, const char *stateDir, int flags) {
char *path;
char *path2;
int fd;
FILE *f;
int i, j;
int rc = 0;
struct alternative *alt;

path = alloca(strlen(stateDir) + strlen(set->alts[0].leader.title) + 6);
sprintf(path, "%s/%s.new", stateDir, set->alts[0].leader.title);
Expand Down Expand Up @@ -770,6 +888,20 @@ static int writeState(struct alternativeSet *set, const char *altDir,
return 1;
}

return 0;
}

/*
* Update the actual symlinks and initscripts for the current alternative.
* Should be called after writeStateConf.
*/
static int writeStatePaths(struct alternativeSet *set, const char *altDir,
int forceLinks, int flags) {
char *path;
int i;
int rc = 0;
struct alternative *alt;

if (set->mode == AUTO)
set->current = set->best;

Expand Down Expand Up @@ -828,6 +960,18 @@ static int writeState(struct alternativeSet *set, const char *altDir,
return rc;
}

static int writeState(struct alternativeSet *set, const char *altDir,
const char *stateDir, int forceLinks, int flags) {
int rc;

rc = writeStateConf(set, stateDir, flags);
if (rc)
return rc;

rc = writeStatePaths(set, altDir, forceLinks, flags);
return rc;
}

static int linkCmp(const void *a, const void *b) {
struct linkSet *one = (struct linkSet *)a, *two = (struct linkSet *)b;

Expand Down
2 changes: 1 addition & 1 deletion mkosi.conf
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Original file line number Diff line number Diff line change
@@ -1,6 +1,6 @@
[Distribution]
Distribution=fedora
Release=41
Release=rawhide

[Build]
BuildDirectory=build/mkosi.builddir
Expand Down