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Improve shmem addstr() and fix possible memory corruption error

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Signed-off-by: DL6ER <dl6er@dl6er.de>
This commit is contained in:
DL6ER
2019-05-25 13:38:19 +02:00
parent 96320db367
commit e1eadb0733
1 changed files with 15 additions and 10 deletions
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25
shmem.c
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@@ -62,22 +62,28 @@ size_t addstr(const char *str)
return 0; return 0;
} }
// Get string length // Get string length, add terminating character
size_t len = strlen(str); size_t len = strlen(str) + 1;
// If this is an empty string, use the one at position zero // If this is an empty string (only the terminating character is present),
if(len == 0) { // use the shared memory string at position zero instead of creating a new
// entry here. We also ensure that the given string is not too long to
// prevent possible memory corruption caused by strncpy() further down
if(len == 1) {
return 0; return 0;
} }
else if(len > (size_t)(pagesize-1))
{
logg("WARN: Shortening too long string (len %zu)", len);
len = pagesize;
}
// Debugging output // Debugging output
if(config.debug & DEBUG_SHMEM) if(config.debug & DEBUG_SHMEM)
logg("Adding \"%s\" (len %zu) to buffer. next_str_pos is %u", str, len, shmSettings->next_str_pos); logg("Adding \"%s\" (len %zu) to buffer. next_str_pos is %u", str, len, shmSettings->next_str_pos);
// Reserve additional memory if necessary // Reserve additional memory if necessary
size_t required_size = shmSettings->next_str_pos + len + 1; if(shmSettings->next_str_pos + len > shm_strings.size &&
// Need to cast to long long because size_t calculations cannot be negative
if((long long)required_size-(long long)shm_strings.size > 0 &&
!realloc_shm(&shm_strings, shm_strings.size + pagesize, true)) !realloc_shm(&shm_strings, shm_strings.size + pagesize, true))
return 0; return 0;
@@ -87,13 +93,12 @@ size_t addstr(const char *str)
// Copy the C string pointed by str into the shared string buffer // Copy the C string pointed by str into the shared string buffer
strncpy(&((char*)shm_strings.ptr)[shmSettings->next_str_pos], str, len); strncpy(&((char*)shm_strings.ptr)[shmSettings->next_str_pos], str, len);
((char*)shm_strings.ptr)[shmSettings->next_str_pos + len] = '\0';
// Increment string length counter // Increment string length counter
shmSettings->next_str_pos += len+1; shmSettings->next_str_pos += len;
// Return start of stored string // Return start of stored string
return (shmSettings->next_str_pos - (len + 1)); return (shmSettings->next_str_pos - len);
} }
const char *getstr(const size_t pos) const char *getstr(const size_t pos)